CERN-SPSC-2004-024
SPSC-M-722 30 August
2004
PHYSICS
WITH
A
MULTI-MW
PROTON SOURCE
CERN,
Geneva,
May 25-27, 2004
Figure
1
Physics with a multi-Megawatt proton
source
Summary
The workshop ‘Physics with a multi-Megawatt (MMW) Proton Source’ was held at CERN on 25-27 May 2004. It was organized by the ECFA/BENE working groups for future neutrino facilities in Europe, and by the EURISOL nuclear physics community to explore the physics opportunities offered by a new high intensity proton accelerator. It confirmed the important synergies that exist between these communities. This document summarises the main design choices for the accelerators and experiments involved, the physics possibilities and the most critical R&D that will be necessary. A preliminary baseline road map is delineated.
A strong and diverse physics programme was highlighted.
The leading particle physics case is provided by the study of neutrino oscillations with the ultimate aim of discovery and study of leptonic CP violation. Two main options emerge.
1) A Neutrino Factory based on a high brilliance muon beam would provide high-energy electron neutrinos (up to 20-50 GeV). Aimed at dense magnetic detectors situated ~700 to 4000 km away, this is by far the best tool to perform very precise and unambiguous measurements of oscillation parameters, neutrino mass hierarchy, CP violation and tests of universality in the neutrino sector.
2) A neutrino beta-beam facility would provide a very clean beam of electron (anti) neutrinos from beta decay of high energy radioactive ion beams of characteristics similar to those of EURISOL. The very large detectors that are required are the same as those needed to extend the search for proton decay and astrophysical neutrinos. In combination with a low energy conventional neutrino beam (superbeam), this would provide interesting sensitivity in search for leptonic CP and T violation.
In addition, the near detectors of these facilities offer the possibility to study neutrino interactions with great precision in various energy regimes. The envisaged proton driver offers great flexibility of time structures and would allow cutting edge experiments in low energy muon physics. It will be of great utility for the high intensity operation of the LHC, and will allow higher intensities to be achieved throughout the present CERN complex and fixed target experiments.
A high intensity proton accelerator has been advocated as opening a wide field of new possibilities in nuclear physics as well, with the availability of intense beams of rare radio-isotopes. The detailed study of properties of nuclei at the edges of stability should project decisive light on the fundamental but still largely mysterious question of nuclear matter and its dynamical symmetries. The simultaneous availability of radioactive ion beams and of low energy muon and antiproton beams should allow a new class of experiments to be performed., several of which are critical for the understanding of star formation and supernovae.
The choices will need to be made in the near future require the critical R&D and studies to be carried out. The list comprises i) the study of high power target, particle collection elements and target stations, ii) the study of beam activations in the proton driver and subsequent accelerators, iii) the demonstration of ionisation cooling, iv) the feasibility study of large underground caverns and v) R&D on the very large detectors that are envisaged.
Table of Contents
1 Foreword: High Energy and High Intensity
Frontiers. 12
2 The High Intensity Frontier. 14
3 Planned High Intensity facilities in the
world. 26
3.1
The Japanese Proton
Accelerator Reseach Center J-PARC.. 26
3.2
U.S. Plans for High Power
Proton Drivers. 29
3.3
Fair, the GSI New
Facility For Antiproton and ion research. 33
4 High Intensity Proton Source. 38
4.1
The future of proton
accelerators at CERN.. 38
4.2
The Superconducting
Proton Linac (SPL) and its potential 43
4.3
The
Rapid Cycling Synchrotron options. 47
5 Facilities around the intense proton
source. 56
5.1
Additional installations
for a neutrino physics facility. 56
5.2
Hadro-production
experiments. 63
5.3
EURISOL : a new nuclear
physics facility. 67
5.4
A neutrino beta beam
facility at CERN.. 70
6 Particle Physics case – neutrino
oscillations. 74
6.1
Overview of neutrino
oscillation physics. 74
6.3
A megaton water Cherenkov
detector 85
7 Other particle physics
opportunities. 98
7.1
Short baseline neutrino
physics. 98
7.2
High intensity muon
physics. 102
7.3
Physics
at Higher Intensity PS or SPS at CERN.. 105
8.1
The future of nuclear
physics studies. 108
8.2
Nuclear dynamics and the
nuclear equation of state. 109
8.3
Astrophysics with
R.I.B. 112
8.4
Fundamental symmetries
and interactions. 116
8.5
New approaches to the
study of the nucleus with muons and antiprotons. 120
9 Conclusions and outlook. 123
10.1 Recommended accelerator R&D.. 132
10.2 Recommended detector R&D.. 133
Workshop Organization, Participants and
Programme. 142
Table of illustrations
Figure 1 Possible layout of the
Superconducting Proton Linac on the CERN site. 15
Figure 2 Possible location of the EURISOL
complex at CERN. 16
Figure 3 Several aspects of physics with
Radioactive Nuclear Beams. 16
Figure 10 Event rates at the exit of the
straight sections in a Neutrino Factory. Note the scale. 23
Figure 12 Principle of the measurement of the
muon EDM.. 24
Figure 14 Artistic aerial view of the Japanese
Proton Accelerator Reseach Complex J-PARC.. 26
Figure 15 Layout of theT2K
experiment 27
Figure 16 The J-Nufact scheme for a Neutrino
Factory, based on a chain of FFAG accelerators 28
Figure 20 The Superconducting Fragment
Separator (Super-FRS) at the
FAIR facility. 34
Figure 23: Expected yields at the Super
Fragment Separator at FAIR. 36
Figure 24 : SPL schematic layout (CDR 1 design
for the superconducting part). 44
Figure 25 : Proton driver complex on the CERN
site. 45
Figure 26: Indicative multi-year planning for
the full SPL project. 46
Figure 27 Rapid Cycling Synchrotron models at
5 GeV (left) and 15 GeV (right) 52
Figure 28 Schematic layout of a Neutrino
Factory. 56
Figure 29 Possible layout of a Neutrino
Factory on the CERN site. 57
Figure 32 Layout of the MICE
experiment. 61
Figure 33 The HARP experiment 63
Figure 34 Transversal momentum resolution as a
function of pT, as
measured by the TPC. 65
Figure 38 : Conceptual layout of the EURISOL
facility. 68
Figure 48 UNO Detector Conceptual
Design. 86
Figure 49 Conceptual Design of Hyper
Kamiokande. 87
Figure 51 Our past, present
and possible future knowledge of nucleon decay. 90
Figure 52 Recent HPD Prototypes from
Hamamatsu. 91
Figure 53 Reference Photosensor R&D in the
USA.. 92
Figure 54: Schematic layout of the inner
detector of a future Large Liquid Argon detector 95
Figure 55 : Artist view of a possible 100 kton
liquid argon TPC. 96
Figure 58 Dm2 atmospheric and
sin2q23 determination at T2K by assuming
present 101
Figure 60 A
sketch of the MEG detector 103
Figure 61
Computed ratio of BRµe/BRµ®eg.
Figure 62 Results
of the SINDRUM II experiment 103
Figure 63 The MECO experiment 104
Figure 72 SPL Block diagram.. 124
Table 1 Performance parameters for Fermilab
and BNL concepts for Proton Driver upgrades. 30
Table 2 Main users’ requests. 38
Table 4 Proton flux in 2010 after
implementation of the improvements recommended by the HIP WG. 40
Table 5
Possible improvement to the accelerator complex. 41
Table 6
Main SPL parameters (CDR 1) 43
Table 7
Linac 4 specifications. 44
Table 8 Parameters
of Existing and Proposed Proton Sources. 47
Table 16 List of participants: 142
1 Foreword: High Energy and High Intensity Frontiers
(R. Aymar, V.
Palladino)
In his welcome address, CERN DG Prof. R.
Aymar outlined his general view of CERN mission and options for the future.
- CERN is the largest particle physics
laboratory in the world, with a history of building and operating accelerators
at the high-energy frontier, like the SPS proton/antiproton Collider, LEP and,
soon, LHC. Along that logic, CERN is now actively pursuing R & D of
CLIC,
- CERN has also a successful tradition of
addressing simultaneously diverse physics issues (fixed target experiments,
neutrinos, radio-active ions, anti-protons) exploiting at best the
capabilities of its accelerator complex. Therefore, the management, with the
support of the Council and the Scientific Policy Committee, is willing to plan
the future in that respect as well.
He welcomed
and thanked all participants for their contribution to the preparation of the
meeting organized for that purpose by the CERN SPSC next September in Villars.
The CERN management will welcome all help in the definition the optimum changes
to be made to the CERN accelerators, so to cover the most ambitious and
promising spectrum of physics experiments.
He outlined
the two driving scientific motivations of a new
vigorous physics program at the high-intensity frontier, and thus
for a new MMW proton facility and this Workshop:
- The discovery of neutrino oscillations has
opened a new window of exploration, unique in several ways. Measured mass
splittings and mixings of neutrinos have been already providing the first
experimental data on physics at higher energy scales. Discovery of leptonic CPV promises
insight into the most fundamental asymmetries of the universe. The accelerator
neutrino community in Europe, now organized also in the BENE network, will do
all efforts to maintain a leading role in the sector of accelerator neutrino
experiments beyond the CNGS. Its present plans should emerge clearly and in
detail.
- The manifestation of the strong and weak interaction in the atomic
nucleus can be rigorously investigated through nuclei with anomalous
proton/neutron ratio.
NuPECC estimates the size of the European community to
be over one thousand scientists and has prioritized two second-generation
facilities with complementary physics reach: GSI-FAIR, based on the In-Flight
separation (IF) method, and EURISOL, based on the Isotope Separator On-Line
(ISOL) method. Among the potential sites for hosting a future high-intensity
EURISOL facility, CERN has unique possibilities of synergy with a neutrino
programme. This workshop should help clarify its extent and determine whether
other physics programmes could also benefit
Among the
possibilities, a superconducting proton linac (SPL) delivering MWatts of beam
power at a few GeV has already attracted the interest of the communities
interested in radio-active ion beams and in neutrinos. It is clear that such an
accelerator could also be beneficial to the whole CERN accelerator complex,
renovating the low energy injectors (Linac 2 and PSB), and increasing
drastically their performance.
Rapid
cycling synchrotrons delivering MMW proton beams at higher energies deserve also
to be considered as alternative or complement to the SPL option. The CERN management would like the help
of all communities concerned to refine the specifications of the future CERN
proton complex to optimize its interest and potential. Additional extensions
should be considered. Comparison with alternative solutions is encouraged.
Needless to say, resources are limited, and convergence among requests has to be fostered. A clear
outlook of the future must be the task of the workshop.
2 The High Intensity Frontier
(A. Blondel,
J. Ellis)
The
last few decades in particle physics have seen the extraordinary success of the
Standard Model, which explains most observed phenomena in terms of gauge
theories. In particular, experiments at the CERN PS and SPS, followed by the
and LEP
Colliders, discovered and studied precisely the Neutral Currents and the
W± and Z bosons. This established the validity of the Standard Model,
the quantum theory of particles and their strong and electroweak interactions,
to distance scales of ~ 10-18m.
Despite these recent successes, a number
of extremely fundamental physics questions remain unanswered. Extensions to the
Standard Model are almost certainly required. Among the most important issues,
one can mention:
- what is the origin of the widely
different masses of elementary particles, and more precisely what is the process
that breaks electroweak symmetry;
- what are the origins of the different
fundamental forces, and can a unified description of the forces be made;
- is the proton
stable;
- what is the origin of matter-antimatter
asymmetry in the universe;
- what is the composition of dark matter,
and the nature of dark energy in the universe;
- what is the dimensionality of space-time and the role of gravity?
Laboratory exploration in particle physics
has traditionally progressed along different and truly complementary lines. The
first one is the high-energy frontier, which has been embodied at CERN by the
S
S, LEP and will soon advance further with the LHC. There is
no doubt that LHC will open a domain of yet unexplored energies and answer a
number of these questions, in particular in the domain of the electroweak
symmetry breaking, addressing the burning issues of the existence and nature of
the Higgs boson and supersymmetric particles.
Many of the other questions require different means of investigations with very detailed studies of the properties of already known particles. This requires well controlled experimental conditions as well as high statistics. In the last few years, the requirements for neutrino physics have led to the study of high intensity neutrino sources, such as the recently published ‘CERN/ECFA studies of a European Neutrino Factory Complex’ [ECFAreport]. Beyond neutrino oscillation physics, this report emphasized the wide interest of a high-intensity complex based on a multi-Megawatt proton accelerator, for studies of rare decays and precise properties of muons and kaons, deep-inelastic scattering with neutrinos, as well as the longer-term possibility of muon colliders. At the same time, the nuclear-physics community, a long-time user of CERN with ISOLDE, has been stressing the virtues of a high- intensity upgrade of the existing facility, with the EURISOL study [Eurisole]. The convergence of interest between the particle-physics and nuclear-physics communities is one of the striking aspects of this high-intensity frontier. Without going into details which will appear in the following chapters, a foretaste of the physics issues is presented in the following.
The leading
possibility for a
high-intensity proton accelerator at CERN is the Superconducting Proton Linac
(SPL). As shown in Figure 1, it could fit nicely adjacent to the CERN site
and feed into the existing CERN infrastructure.
Figure 1 Possible layout of the Superconducting Proton Linac on the CERN site.
As discussed in chapter 4 , (see, in particular , Table 2) a survey [HIP_web] has shown that the high-intensity requirements from CERN users cover the CNGS and fixed-target programme, the LHC upgrade, and on a more ambitious scale, the nuclear-physics community, and the high intensity particle physics programme in neutrino, muon and kaon physics in particular.
Clearly, ensuring that the LHC can reach the highest possible luminosity will be of tremendous importance, especially if this can be achieved in a way which is convenient to the experiments (avoiding excessive pile-up of events) while minimizing the integrated radiation dose in the vicinity of the experiments. Although it is not entirely clear at the moment how this can be best achieved, the flexibility offered by a high brilliance proton source with flexible time structure will in all likelihood be very valuable.
2.1 Nuclear physics
As shown in Figure 2, the SPL protons could be served to an important
complex of Radioactive Ion Beams (RIB), EURISOL, which is described in detail in
section 5.3. The Isotope Separation On-Line (ISOL) technique to
produce radioactive beams has clear complementary aspects to the In Flight
Fragmentation (IFF) method which will be used at the project FAIR recently
approved in GSI (see section 3.3). First-generation ISOL-based facilities have
produced their first results and have been convincingly shown to work.
EURISOL aims at
increasing the variety of radioactive beams and their intensities by orders of
magnitude over the ones available at present. As shown in Figure 3, this will offer rich opportunities for various
scientific disciplines including fundamental nuclear physics, nuclear
astrophysics and the study of fundamental symmetries, as well as a number of
other applications (radioactive spies, curing chemical blindness, positron
annihilation studies, applications to biomedicine, etc).
Figure 2 Possible location of the EURISOL complex at CERN.
Figure 3 Several aspects of physics with Radioactive Nuclear Beams.
2.1.1
Fundamental nuclear
physics.
Although
nuclei can be seen as composed of few well known elements bound by a well-known
force, the resulting complexity is such that many fundamental questions remain
unanswered. In particular it is not clear what are the boundaries of the domain
in which nuclei are stable, either at the neutron and proton drip lines, or in
the limit of super-heavy elements.
Establishing the limit of nuclear existence involves rare reactions and thus
will require the very high intensities that EURISOL would allow.
Among
other fundamental questions, one can cite the role played by nucleon pairing
(nucleonic cooper pairs), the appearance and behavior of neutron haloes and
skins in neutron-rich nuclei, and more generally the modification of shell
closures and magic numbers in the vicinity of the drip-lines (see sections 8.1 and 8.2).
2.1.2 Nuclear Physics and Astrophysics
Many phenomena in the universe, such as novae and supernovae, X-ray busts, black hole formation or primordial nucleo-synthesis, represent nuclear experiments on a grand scale, often under conditions that – at least for the time being – cannot be replicated on earth. Nuclear physics is an essential provider of the experimental and theoretical data which are needed to model these phenomena. Figure 5 illustrates this point and describes the path through largely unknown nuclear regions that the nuclear reactions follow to produce the heavier nuclei. The most important parameters needed to be able to improve these calculations are nuclear masses (including n- and p-separation energies) near the proton drip-lines, b-decay half-lives along the process paths and n- and p-capture rates on ‘short-lived’ nuclei. As discussed in chapter 8.3, many of these data are very poor or completely missing at present and the whole field would benefit considerably from systematic data and understanding of these processes.
Figure 5 Novae and Supernovae constitute nuclear reactions at a grand scale.
The explanation of the energy production in explosive thermonuclear burning
probably requires two distinct neutron-capture processes as the origin of heavy
nuclei beyond iron.
2.1.3
Other
applications
As will be discussed in
section 8.4, the availability of intense beams of various nuclei,
but also pions and muons should allow very precise search for violations of
fundamental symmetries. Among these one could cite the search for neutron and
muon electric dipole moment (EDM), search for T violation in beta decay (using
reconstruction of final-state momenta and spin polarisation). Also the search
and study of rare or forbidden nuclear decays should be of great interest to
improve the understanding of nuclear matrix elements, possibly shining some
light on those necessary for the interpretation of neutrino-less double beta
decay.
The combined availability
of intense of radioactive ion beams with intense muon or antiproton sources
opens the very interesting possibility of probing nuclear matter with muonic and
anti-protonic atoms, in which the nuclei is already rare or unstable. This
technique is both a probe of the structure of these nuclei, as well as a means
to produce nuclei one or several steps closer to the drip lines (section 8.5).
Finally one cannot close
this discussion on nuclear physics without mentioning the industrial
applications such as radioactive spies, curing chemical blindness, positron
annihilation studies, applications to biomedicine, and material science that
benefits from intense beams of radioactive ions, neutrons and
muons.
2.2
Particle physics
The leading
particle-physics motivation for a high-intensity proton driver is the study of
neutrino oscillations, but the facility would also offer great opportunity for
the neutrino, muon and kaon physics. Last but not least, a Neutrino Factory
would be the first step towards muon colliders.
2.2.1
Neutrino oscillations
The observation of neutrino oscillations has now established beyond doubt that neutrinos have mass and mix. This existence of neutrino masses is in fact the first solid experimental fact requiring physics beyond the Standard Model. It was soon realized that with three families and for a favourable set of parameters, it would be possible to observe experimentally violation of CP or T symmetries in the neutrino oscillation phenomenon [Ruj99]. This observation reinforced the already considerable interest for precision measurements of neutrino oscillation parameters. We know since 2003 and the results from SNO and KAMLAND [SNO02], [Kamland02] that the neutrino parameters belong to the so-called LMA solution which suggests that Leptonic CP violation should be large enough to be observed in high-energy neutrino oscillation appearance experiments.
Figure 6
Graphical representation of the present knowledge of the neutrino mixing matrix.
The rotations by the successive Euler angles q12, q13, q23
that
transform the mass eigenstates n1 n2
n3 into the flavour
eigenstates ne nm nt are shown on the left, while the mass
splittings are shown on the right. The best present values are
q12 =320, q23 = 45
0, q13 < 130, and
Dm212 = + 8
10-5 eV2,
Dm223 =
± 2.5
eV2. In addition there is a phase,
d, which generates CP and T violating
effects in neutrino oscillations.
Figure 7 Present determination of
the neutrino mixing parameters. Left:
q23 and Dm223 from
atmospheric neutrinos and the K2K experiment; right: q12 and Dm212 from the solar neutrinos and the KAMLAND
experiment [neutrinofits].
The fact that neutrinos have masses that are so much smaller than those of the other known fermions (12 orders of magnitude smaller than the electroweak mass scale or the top quark mass) is a mystery that could open the way to the solution of a number of fundamental questions. One can find a more or less natural explanation in the so called ‘See-Saw’ mechanism [seesaw]. In this scenario, the neutrinos are very light because the observed light neutrinos are low-lying states of split doublets with heavy neutrinos of a mass scale M which is interestingly similar to the grand unification scale:
mn M = v2
with v » mtop » 174 GeV Þ M
£ O (1015 )
GeV
The
combination of this scenario with the fact that neutrinos could violate CP
symmetry opens the fascinating possibility to explain is simple terms the
matter-antimatter asymmetry of the universe [leptogenesis], if for instance the
decays of heavy Majorana neutrinos violate CP violation, in a way similar to
what happens in K0L decays:
N ® ℓ+X ¹ N ® ℓ-X,
with the
resulting lepton-antilepton asymmetry propagating into a baryon-antibaryon
asymmetry.
Clearly the study of neutrino properties and in
particular the search for leptonic CP violation is a subject of the highest
scientific priority.
The tools
of choice to search for leptonic CP violation are the oscillations 
, and at a later stage 
. The search for an asymmetry between neutrino and
anti-neutrino oscillations requires dedicated experiments with high statistics
and well-defined flux. Solar
neutrinos and reactor neutrinos are
of too low energy to allow appearance experiments, and atmospheric neutrinos
being an intrinsic mix of neutrinos and anti-neutrinos are inadequate.
Invariably, the requirement of high flux accelerator-generated neutrino beams
leads to the need for a high-intensity proton source.
Several
possibilities exist for neutrino oscillation experiments. First the CERN to Gran
Sasso beam, which is optimized for the search for the
appearance, would certainly benefit from an increased
availability of protons. Then, using more directly the SPL, have been envisaged
the following possibilities: the low energy superbeam [Gomez01], beta-beams
[Zucchelli], and the Neutrino Factory [Geer98], as sketched on Figure 8.
Figure 8 Three possible neutrino facilities based on the same proton driver. Top: a low energy conventional pion decay beam; middle the beta beam where 6He and 18Ne RIBs are accelerated using the PS and SPS as accelerators; bottom, the neutrino factory where muons are accelerated and stored at 20-50 GeV.
The superbeam and beta beam have the advantage of having similar energies which allows usage of the same far detector that could be located for instance in a new international laboratory in the Fréjus tunnel (see sections 6.2, 6.3 and 0). A comparison of performances of these options is made in Figure 9. All three proposals are superior to existing or planned facilities in the world, but the Neutrino Factory is clearly a much more powerful device. It must use a different detector, however, and may be more difficult and expensive than the others. As pointed out in chapter 6.1.3, using a high energy beta-beam could partly compensate the performance deficit of the low-energy one, but the technical and financial implications have not yet been established.
Figure 9 relative sensitivity to q13 (top) and to the CP violating phase
d (bottom), of various options of Figure
8 for future neutrino facilities based on a high
intensity proton driver.
2.2.2 High-precision neutrino scattering
As discussed in [Mangano01],
[Bigi01], the neutrino beams at the end of the straight section of a neutrino
factory offer an improvement in flux by several orders of magnitude over
conventional beams, allowing several times 108 events to be collected
per kilogram and per year. (Figure 10). This could allow a new generation of neutrino
experiments, where very detailed studies of nucleon structure, nuclear effects,
spin structure functions and final state exclusive processes can be made. Also
precision tests of the Standard Model could be carried
out in neutrino
scattering on nucleon or electron target, as well as a precise determination of
neutrino cross-sections and flux monitoring with permil accuracy.
Figure 10 Event rates at the exit of the straight sections in a Neutrino Factory. Note the scale.
As discussed in chapter 7.1, in the case of a superbeam or beta beam, the study of low-energy neutrino interactions in a near detector is mandatory for the sake of the oscillations analysis. In addition, the understanding of the low-energy transition from elastic reactions to the resonance region and the deep inelastic region is in great need of accurate data.
2.2.3 Muon physics
A high-intensity proton source could
certainly produce many low-energy muons and thus, provided the beam and
experiments can be designed to do so, provide opportunities to explore rare
decays, such as 
, 
, or the muon conversion 
, which are lepton-number-violating processes. While the
See-Saw mechanism provides a very appealing explanation of neutrino masses and
mixings, its inclusion in supersymmetric models almost invariably leads to
predictions for these processes that are in excess or close to the present
limits.
that are close to or even beyond the present limits of
~10-11 .It is therefore quite possible that one of these processes will be discovered in the upcoming generation of experiments (MEG at PSI, MECO at BNL) in which case a detailed study would become mandatory. If not, further search with higher sensitivity would be in demand. It should be emphasized that the three processes are actually sensitive to different parameters of these models, and thus complementary from both the experimental and theoretical points of view.
Another fundamental search would clearly be the search for a muon electric dipole moment (EDM), which would require modulation of a transverse electric field for muons situated already at the magic velocity where the magnetic precession and the anomalous (g-2) precession mutually cancel.
Figure 12 Principle of the measurement of the muon EDM
2.2.4 Kaon physics
Kaons have played a fundamental role in the
discovery of both parity violation and CP violation. Despite the great advance
due to B factories, there is a growing interest in challenging channels such as
, and 
, which is a CP-violating process.
Discovery or precision study of these processes constitute further test of our
understanding of CP violation in the quark sector.
In addition the search for rare processes
such as 
is
a sensitive probe of new physics.
Figure 13
Left, the dependence of the rare decays
, and
upon the parameters of the unitarity
triangle; right, sensitivity of 
to
the Susy mass scale m0 .
2.2.5 Muon Colliders
Finally, although it was not discussed a the workshop, it is worth keeping in mind that the Neutrino Factory is the first step towards muon colliders. As shown in [muoncollider], the relevant characteristics of muons are that, compared to electrons, i) they hardly undergo synchrotron radiation or beamstrahlung, ii) their coupling to the Higgs bosons is multiplied by the ratio (mm/me)2 , thus allowing s-channel production with a useful rate.
These remarkable properties make muon colliders superb tools for the study of Higgs resonances, especially if, as predicted in supersymmetry, there exist a pair H,A of opposite CP quantum numbers which are nearly degenerate in mass. The study of this system is extremely difficult with any other machine and a unique investigation of the possible CP violation in the Higgs system would become possible.
2.3 Conclusions
A proton accelerator of multi-Megawatt power would offer a very strong physics case with opportunities for a large variety of cutting-edge experiments. It is synergetic with the CERN middle-term programme providing an upgrade of the LHC luminosity as well as the intensity of the fixed-target programme. It allows one to envisage a long-range neutrino-physics programme, with superbeam, beta-beam and/or Neutrino Factory, and a complementary high- intensity muon physics programme, possibly leading to muon colliders. In addition, it is the backbone of the next generation facility for nuclear physics with important consequences for astrophysics and precision tests of the Standard Model. It certainly constitutes an interesting project – and CERN would be a good place for it!
3 Planned High Intensity facilities in the world
3.1 The Japanese Proton Accelerator Reseach Center J-PARC
(S. Nagamya, V.
Palladino)
After the groundbreaking ceremony of June 2002, the
centre is in advanced state of construction at the JAERI site in Tokai, on the
Pacific coast, about 2 hours NE of Tokyo. Once completed, the complex (Figure 14) will comprise a 350 m long Linac, a 1 MW
3
GeV Synchrotron
at
25 Hz, and a 0.75 MW 50 GeV Synchrotron.
It will be a multipurpose installation serving four different facilities:
Nuclear Transmutation, Materials and Life Science, Nuclear & Particle
Physics and Neutrino to Superkamioka [Fukuda98].
Figure 14 Artistic aerial view of the Japanese Proton Accelerator Reseach
Complex J-PARC
The
Nuclear Transmutation facility will operate at 0.6 GeV. The proton beam at 3 Gev
will drive a source of separated radioactive nuclei source and the high
intensity pulsed Japanese spallation neutron source (JSNS) whose 23 neutron beam
lines will be exploited by the Materials and Life Science facility (magnetism,
fractals, polymers, structural biolgy etc). The beam 50 GeV will produce 1) high
intensity muon beams from pion decay, for fundamental and applied muon science
2) hadronic beams (pions, kaons, antiprotons etc) to study mesons in nuclear
matter, rare kaon decays, hyper-nuclei, antimatter 3) a conventional neutrino (super)beam for the study of
neutrino oscillations.
The
approved neutrino oscillation program [T2K] is based on a conventional
nm superbeam
derived from the 50 GeV synchrotron. It has become known as the T2K (Tokai to
Kamioka) project (Figure
15), successor of the K2K (KEK to Kamioka) experiment
[K2K] that has confirmed, with man made laboratory neutrinos, the phenomena of
nm disappearance
first observed in the Kamioka detectors with atmospheric neutrinos. The T2K
neutrino flux will be about 100 times larger that K2K’s. nm disappearance,
presumably dominated by the transition into nt ,
will be studied with superior precision. The compelling search of the
subdominant transition into ne ,
that promises the answers to the remaining and most intriguing questions
concerning neutrino mixing, will be possible with unprecedented
sensitivity.
Figure 15 Layout of theT2K experiment
If transition nm, to
ne are
discovered in the first phase of T2K and if it will prove possible to run the 50
GeV accelerator at significantly higher power, the project may have a second
phase with a 50 times larger Hyper-Kamiokande detector, 1 Mton or so, aiming at
discovery of leptonic CP violation.
Construction
of all elements of the complex has started. In spite of different causes of
delay, among them the lucky discovery on site of invaluable archeological
findings from the Japanese middle ages, accelerator beams are expected to be
operating by the end of 2007 and the experimental facilities will be coming into
operations early in 2009, at the latest, when the
neutrino
superbeam will also start operation. The total capital cost will be 151 GYens,
grossly equivalent to 1.5 G$, for the first seven years phase. This is still
mostly still to be spent, in the years 2004-2009; about 80% of purchase
commitments are done, however. The cost will rise to 189 GYens, when including
its phase II after 2009.
The origin of the JPARC is rooted in
the 1998 negotiations and in 1999 MOU between the Japanese applied nuclear
physics (JAERI) and particle physics (KEK) agencies. Strongly encouraged in the
following years, under the auspices of the newly established fundamental &
applied science & technology joint MEXT ministry, the project obtained the
construction budget for its first phase in 2001. Notably, however, ideas for a
joint large hadron facility project have to be traced, at least back to
1985!
A first call in 2002 resulted in 30
LOI [jparclois], signed by 478 physicist, about 2/3 non- Japanese. The call for
proposal is expected in 2004 An International Advisory Committee (IAC) has long
been in place.
On
October 30, 2003,the LINAC had a successful acceleration of 6 mA at 20 MeV. On
November 7, 30 mA was achieved. Among the recent realizations are the vacuum
pipe for the 3 GeV beam and the first RF cavities, dipole and quadrupole magnets
for the 50 GeV beam. Impressive progress in construction was manifest from
pictures taken at the annual meeting of the IAC in March 2004.
Due
to financial difficulties, the energy of the front end LINAC will be initially
limited to 200 MeV, but work towards its upgrade to the original 400 MeV will
start immediately after. This will result in a delay in the achievement of the
target intensity (1 MW at 3 GeV and 0.75 MW at 50 GeV) of the first phase.
Achieving higher intensities, up to 4 MW, represents one of the major challenges and unknowns for the
successive phases of the facility.
Figure 16 The J-Nufact scheme for a Neutrino Factory, based on a chain of FFAG accelerators
The
number of facilities is also expected to evolve. It is worth mentioning, because
relevant to the neutrino sector, that preliminary plans have been outlined,
following an independent and original Japanese scheme [Jnufact], to use the high
intensity muon area as the front end of a neutrino factory (Figure
16).
3.2
U.S.
Plans for High Power Proton Drivers
(S. Holmes)
3.2.1 Motivations
A “proton driver” is defined as an accelerator capable of delivering beam power in excess of 1 MW onto a target, derived from a proton beam of at least 1 GeV. A broad range of motivations for high intensity proton drivers exist as described by Ellis [Ellis04]. Within the United States both Fermi National Accelerator Laboratory (Fermilab) and Brookhaven National Laboratory (BNL) are developing concepts for proton drivers with 1-2 MW of beam power [Weng03],[Fermi02]. For Fermilab and BNL, with traditions in high energy and nuclear physics, the motivations center around neutrino physics, rare kaon and muon decays, pulsed neutrons, and/or ultimate utilization as an injector into a hadron collider beyond the Large Hadron Collider at CERN.
3.2.2
U.S. Design
Concepts
The Fermilab and BNL concepts for 1-2 MW proton drivers have several elements in common:
1.
An increase in the
repetition rate of an existing accelerator, the Main Injector in the case of
Fermilab, and the AGS in the case of Brookhaven.
2.
An increase in the injected
beam intensity through construction of a new linac (or possibly a
synchrotron).
3.
A decrease in the filling
time of the existing machine. (This is most straightforwardly accomplished by
utilizing a linac rather than a synchrotron.)
4.
Reliance on previously
developed superconducting rf technologies.
5. Upgrade paths are identified that could yield additional factors of 2 to 4.
The BNL concept features a 1.2 GeV superconducting linac as the injector into the upgraded AGS. This configuration would allow the delivery of 1 MW of beam power from the AGS at 28 GeV. Fermilab has two implementations under evaluation, each with the capability of providing high power beams simultaneously at 120 GeV, from the Main Injector, and at 8 GeV. The two possibilities are an 8 GeV synchrotron or an 8 GeV superconducting linac, with the linac preferred.
Performance goals and underlying parameters for the various concepts are shown in Table 1. The columns labelled “Present” represent typical performance with the currently configured accelerator complex.
Table 1 Performance parameters for Fermilab and BNL concepts for Proton Driver upgrades.
|
|
|
Fermilab
Options |
|
Brookhaven |
|
| |||
|
|
|
Present |
Synchrotron |
Linac |
|
Present |
AGS
Upgrade |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Linac |
|
|
|
|
|
|
|
|
|
|
Kinetic
Energy |
|
400 |
600 |
8000 |
|
200 |
1200 |
|
MeV |
|
Peak
Current |
|
40 |
50 |
25 |
|
40 |
30 |
|
mA |
|
Pulse
Length |
|
90 |
90 |
1000 |
|
60 |
720 |
|
msec |
|
Protons/pulse |
|
2.3E+13 |
2.8E+13 |
1.6E+14 |
|
1.5E+13 |
1.0E+14 |
|
|
|
Repetition Rate
|
|
15 |
15 |
10 |
|
15 |
2.5 |
|
Hz |
|
Average Beam
Power |
|
0.02 |
0.04 |
2.00 |
|
0.007 |
0.05 |
|
MW |
|
|
|
|
|
|
|
|
|
|
|
|
Booster |
|
|
|
|
|
|
|
|
|
|
Kinetic Energy
(Out) |
|
8 |
8 |
|
|
1.5 |
|
|
GeV |
|
Protons per
Pulse |
|
5.0E+12 |
2.5E+13 |
|
|
1.5E+13 |
|
|
|
|
Repetition Rate
|
|
7.5 |
15 |
|
|
6.7 |
|
|
Hz |
|
Protons/hour |
|
1.4E+17 |
1.4E+18 |
|
|
3.6E+17 |
|
|
|
|
Average Beam
Power |
|
0.05 |
0.5 |
|
|
0.02 |
|
|
MW |
|
|
|
|
|
|
|
|
|
|
|
|
Main
Injector |
|
|
|
|
AGS |
|
|
|
|
|
Kinetic Energy
(Out) |
|
120 |
120 |
120 |
|
24 |
28 |
|
GeV |
|
Protons per
Pulse |
|
3.0E+13 |
1.5E+14 |
1.6E+14 |
|
6.0E+13 |
9.0E+13 |
|
|
|
Repetition Rate
|
|
0.54 |
0.65 |
0.67 |
|
0.33 |
2.50 |
|
Hz |
|
Protons/hour |
|
5.8E+16 |
3.5E+17 |
3.8E+17 |
|
7.2E+16 |
8.1E+17 |
|
|
|
Average
Beam Power |
|
0.3 |
1.9 |
2.0 |
|
0.1 |
1.0 |
|
MW |
3.2.3 The Brookhaven AGS Upgrade
The Brookhaven AGS upgrade is based on the direct injection of approximately 1´1014 protons via a 1.0 GeV superconducting extension to the existing 200 MeV drift tube linac. The extension bypasses the existing 1.5 GeV Booster currently used for injection into the AGS. The injector upgrade is accompanied by modifications to the AGS rf and power supply systems to enable 2.5 Hz operations. The net result is a factor of ten increase, to 1.0 MW, in the beam power available at 28 GeV. Subsequent upgrades of either the linac intensity, to 2´1014, and/or the repetition rate, to 5 Hz, would enable additional factors of 2-4 in delivered beam power. A schematic view of the AGS upgrade is given in Figure 17.
Figure 17 Schematic view of the AGS upgrade concept. Existing accelerators are in red, new facilities are in blue
3.2.4 The Fermilab Proton Driver
The goal of the Fermilab Proton is to increase the intensity delivered to the Main Injector to approximately 1.5´1014 protons, allowing full exploitation of the large aperture of the Main Injector and enabling, following relatively modest upgrades to the MI, 2 MW of beam power delivered at 120 GeV. Inspired by the outstanding successes of the TESLA program [Tesla01] the idea has emerged of an 8 GeV superconducting proton linac, injecting H- directly into the Main Injector. The linac concept is represented schematically in Figure 18. The concept utilizes technologies currently under development for both the RIA and TESLA proposals. A number of variations on this basic scheme are still being explored including: 2.0 MW beam power at 8 GeV, frequencies based on 1207.5 MHz and derivatives thereof, and a warm front end. The key element in the design is the utilization of a “TESLA style” rf distribution system in which 36 cavities are driven from each klystron. Realization of this design configuration is dependent on the development of a ferrite based phase/amplitude controller. In addition, the utilization of such controllers would allow the acceleration of electrons interleaved with proton cycles in the downstream 7 GeV of the linac.
Figure 18 Schematic layout of the superconducting linac based Proton Driver at Fermilab. Linac variants under consideration include higher beam power (2 MW), lower rf frequencies (1207 MHz and its derivatives), and a warm front end.
3.2.5 Summary
Design concepts for Proton Drivers operating in the range 1-2 MW are being developed by both BNL and Fermilab. Both laboratories are motivated by a variety of physics opportunities, with neutrinos in the forefront. Active R&D programs are underway on critical components, aimed at demonstrating technical and cost performance. The recently released Fermilab Long Range Plan [Lrplan04] identifies a 2 MW Proton Driver as the preferred option in the event a linear collider is constructed elsewhere or is delayed. To that end, Fermilab is currently preparing documentation sufficient to support a “statement of mission need”, know as Critical Decision 0 within the U.S. Department of Energy project management system. Brookhaven is preparing a design study that could serve as the basis for a subsequent proposal.
3.3 Fair, the GSI New Facility For Antiproton and ion research
(H.-J.
Kluge)
The physics program at the future international facility FAIR at Darmstadt (Facility for Antiproton and Ion Research) addresses a broad research spectrum: In hadron and nuclear physics, it ranges from studies of the sub-nuclear degrees of freedom, of the origin of the nuclear force and the quark-gluon structure of extended nuclear matter, to the exploration of the structure of nuclei, the nuclear many-body system, far from stability. Furthermore, other fields of physics will be exploited such as quantum electrodynamics in extreme electromagnetic fields, atomic physics and fundamental tests by use of antiprotons, the physics of dense plasmas or materials science and biophysics.
The tools for the FAIR research program are intense primary and secondary ion beams, including beams of antiprotons. These beams are generated in the FAIR facility (Figure 19) which makes use of the existing Unilac-SIS18 accelerator as injector. For antiproton production, a linear proton injector and accelerator will be added. The double-ring synchrotrons SIS100/300 will provide a major step in primary and, thus, in secondary ion beam intensities and, for certain demands, also in beam energy. Since the present synchrotron SIS18 is already at its space charge limit of about 1010 ions per second with beams of highly stripped uranium U73+, two steps are foreseen to increase the intensity by two orders of magnitude: a faster cycling of the injector (from 0.3 Hz to 3 Hz) and the use of a lower charge states as, for example, q = 28+ for the case of uranium.
Figure 19 Schematic layout for the Facility for Antiproton and Ion Research,
FAIR, at GSI. Details are given in the CDR [CDRFair].
To achieve 1.5 to 2.0 GeV per nucleon for the secondary radioactive beams, an accelerator ring with correspondingly higher magnetic rigidity (≈ 100 Tm) is required. The SIS100 synchrotron will also provide 30 GeV protons, the optimum energy for antiproton production. The second ring, SIS300, serves as a stretcher for slow extraction with high duty cycle and for high charge-state heavy ions and provides energies up to 35 GeV per nucleon at somewhat lower intensities for nucleus-nucleus collisions.
The science case has been worked out in detail in the Conceptual Design Report (CDR) for the facility [CDRFair]. Within the context of this workshop, discussing a high-power proton driver, there is an overlap of FAIR with such a MEGAWATT Facility in the case of research programs with beams of short-lived nuclei. Therefore, the following discussion will be focused on the production and on experiments with radioactive beams (RIB).
Figure 20 presents the layout of the facility for RIB production, separation, and experiments with such beams. The central instrument is the large-acceptance high-resolution spectrometer for exotic nuclei, a two-stage super-conducting fragment separator, called Super-FRS, plus three areas for experiments with stopped (or slowed-down), with fast, and with stored and cooled beams. A key requirement for obtaining uncontaminated secondary beams is the high energy of the primary heavy-ion beam.
Figure 21 shows existing or planned facilities for in-flight production and separation of RIB and indicates at what energy per nucleon the secondary products are fully stripped from electrons that leads to a clean m/q = m/Z separation. The benefit of primary heavy-ion beams well above 1 GeV/nucleon is evident. Important features of in-flight production of RIB are that the radionuclides are available for experiments irrespective of their chemical properties, and that the half-lives of the accessible radionuclides are only limited by their time of flight from the production target to the detector. For relativistic RIB, this time span is of the order of microseconds.
Figure 20 The Superconducting Fragment Separator (Super-FRS) at the
FAIR
facility.
Figure 21 In-flight radioactive beam facilities and yields of fully stripped
ions as a function of energy.
An example for production and identification of RIB is shown in Figure 22. In this case, a 1 GeV/u uranium beam impinged on a hydrogen target of the present fragment separator FRS at GSI. Over 1000 reaction products could be separated and identified. This fast and universal production mechanism is complementary to the isotope separator on-line (ISOL) approach which has the advantage of higher production yields, as compared to the in-flight technique, for longer-lived radio-nuclides of volatile elements which are released quickly from the target matrix.
Figure 22 Production of secondary beams by 1 GeV/u uranium ions impinging on a
hydrogen target. Over 1000 products were identified by the fragment separator
FRS at GSI.
A second key feature of FAIR is cooling
and storage. This technology is going to play an important role at the future
facility, for radioactive ion beams as well as for high-energy anti-protons.
Beam storage and cooling for high-energy heavy-ion beams has evolved at the
present GSI facility as a technology with novel applications and research
opportunities [STORI02].
Presently, nuclear physics experiments by use of the Experimental Storage Ring, ESR, at GSI concern mainly mass spectrometry and lifetime measurements. In the future, reaction experiments in inverse kinematics will play a major role. Here, stored and cooled highly-charged radioactive ions react with the atoms of the gas jet target installed in the storage ring. In this context, it should be noted that acceleration by synchrotrons and, in this way, production of pulsed beams of radionuclides are perfectly tailored for highly efficient injection into storage rings. Storing and cooling of radionuclides are effective means to increase the luminosity for reaction experiments by many orders of magnitude since one gains by the factor of the revolution frequency (typically 1 MHz) and the extremely small diameter of the cooled circulating ion beams.
Therefore, also nuclei very far from stability, which are produced with very low yields at FAIR, will become accessible to experimental investigation. The yields expected at the FAIR facility are shown graphically in the chart of nuclei of Figure 23. Here, the known isotopes are enclosed by a black line. The red lines indicate possible routes of the r-process. High yields of up to 106 will be available for more detailed studies of presently known nuclei over nearly the whole chart of nuclei. It is evident that highly efficient detection techniques are required to expand our knowledge to shorter-lived nuclei farther away from stability.
Figure 23: Expected yields at the Super Fragment Separator at FAIR.
4 High Intensity Proton Source
4.1 The future of proton accelerators at CERN
(R. Garoby, W.
Scandale)
The Large Hadron
Collider will be filled through a set of high performance proton accelerators
providing the high brightness beam needed to reach the foreseen luminosity.
Although this difficult project has top priority and uses most of the CERN
resources, it is nevertheless time investigating improvements of the proton
accelerator complex for physical cases beyond the LHC expectations. The needs of
multiple physics communities have to be taken into account, as well as the
necessity of consolidating the installations while keeping high reliability.
This paper starts from the analysis and proposals made by the “High Intensity
Proton” (HIP) working group [Hip_web],
[Benedikt04] to improve the performances of
the PS and the SPS complex and better match the users requests in a staged
scenario at short and medium term, and complement it, addressing the main
possibilities beyond that horizon.
4.1.1
Outcome
of the High Intensity Protons Working Group
The HIP working
group, mandated by the direction of the AB department, has recently established
a list of requests from the physics teams already working at CERN and
recommended a path for the upgrade of the proton accelerators [Hip_web],
[Benedikt04]. The needs of LHC, COMPASS, neutrino and radio-active ion beam
physics have been taken into account. For the other present users, i.e. AD, PS
East area and nToF, the assumption has been that their requirements do not
significantly influence the choice, and that every upgrade scenario would be
compatible. In terms of schedule and resources, the requests fall into three
main categories: (i) the short term, “low” (ideally zero) cost demands, which
match the present commitments of CERN and belong to the approved physics
programme, (ii) the medium term, “medium” cost requests, which correspond to
modest and progressive increases of performance for the present experiments,
(iii) the long term, “high” cost
wishes, which are linked to major equipment upgrades and to new
experiments suggested for integration inside the future physics programme of
CERN. These are summarised in Table
2.
Table 2 Main users’ requests
|
User |
CERN
commitment* |
Users’
wishes | |
|
Short
term |
Medium
term [~asap!] |
Long
term [> 2014] | |
|
LHC |
Nominal
luminosity 1034
cm-2s-1 |
Ultimate
luminosity 2.6´1034
cm-2s-1 |
Luminosity
upgrade (tenfold) |
|
SFT
(COMPASS) |
4.3´105
spills/year? |
7.2´105
spills/year |
|
|
CNGS |
4.5´1019
p/year |
Upgrade
~ ´
2 |
|
|
ISOLDE |
1.92
μA** |
Upgrade
~ ´
5 |
|
|
Future
n
beams |
|
|
>
2 GeV, 4 MW |
|
EURISOL |
|
|
>
1-2 GeV, 5 MW |
*
Reference value for analysis. ** 1350 pulses/hour –
3.21013 protons per pulse (ppp).
The Linac2, PSB,
PS and SPS have been built more than 35 years ago. Although a significant
fraction of their equipment has been renovated, the most expensive ones are the
oldest and show weaknesses. This has been aggravated by the reduction or even by
the suppression of preventive maintenance due to the lack of resources during
the past years. Therefore consolidation is essential in the near future and, in
the medium term, the replacement of these accelerators deserves serious
consideration. Moreover, the reduction of beam losses is a major issue in order
to minimize the material irradiation for improved reliability and, even more
important, the dose taken by the personnel during
maintenance.
The analysis of the proton flux available to
the users starts in 2007, corresponding to the first year of LHC operation,
under the following assumptions:
o
Accelerators operating time
per year
PS: 5400 h (without
setting-up)
SPS/LHC: 4700 h
(without setting-up)
SPS in LHC filling
mode: 15% (5%) of the time
SPS in LHC pilot
mode: 35% (10%) of the time
SPS in CNGS&SFT
mode: 50% (85%) of the time
o
Availability
PS & PSB:
90%
SPS :
80%
o
Beam
intensities
SPS for CNGS:
4.4´1013 and
7´1013
ppp
PS for CNGS:
3´1013 and
4´1013
ppp.
The LHC pilot beam
is a “safety beam” to be used to establish circulating beam. The following supercycles have been
assumed:
o
LHC filling super-cycle:
1 LHC filling (flat
porch for 4 PS injections), nominal length ³ 21.6
s
o
LHC pilot
super-cycle:
1 LHC pilot + 2
CNGS, nominal length: 22.8 s
o
CNGS&SFT super-cycle:
3 CNGS + 1 SFT + 1
MD (Machine Development), nominal length: 34.8 s.
Without any
improvement, the basic requests cannot be met, especially for the ISOLDE and SPS
users (Table
3 illustrates a case where priority is given to CNGS,
resulting in a low flux for COMPASS). Moreover, the large level of beam loss
associated with the CNGS operation in the PS will cause irradiation of PS
equipment with detrimental consequences on reliability and
maintenance.
Table 3 Proton flux in 2007 without improvement to the accelerators (“pot” stands for protons on target).
|
|
Available
flux |
Basic user’s
requests |
|
|
CNGS
flux |
4.4 |
4.5 |
1019
pot/year |
|
COMPASS
spills |
1.9 |
7.2 |
105
/year |
|
ISOLDE flux
|
1.75
[1215] |
1.9
[1350] |
(μA)
[pulses/hour] |
|
PS East area
spills |
1.5 |
1.3 |
106
/year |
|
nToF
flux |
1.7 |
1.5 |
1019
pot/year |
Having considered
the possible solutions, the following recommendations are
made:
·
In the short term, define in
2004 and start in 2005 three projects: (i) a new multi-turn PS extraction, to
reduce beam loss and activation, (ii) an increased intensity in SPS for CNGS
(implications in all machines), (iii) the reduction from 1.2 s to 0.9 s of the
PSB minimum repetition time.
·
In the medium term, design of
a new linac (“Linac4” [Garoby04]) for the replacement of Linac2, with the goal
of preparing for a decision of construction at the end of
2006.
·
In the long term, prepare for
a decision concerning the optimum future accelerators by pursuing the study of a
Superconducting Proton Linac [Spl_web], [Vretenar00] and by exploring
alternative scenario for the LHC upgrade.
The estimated
performance resulting from the implementation of the short and medium term
measures is shown in Table
4. Numbers without parenthesis can be obtained by
giving the highest prioritys to CNGS. Conversely, the numbers in parenthesis are
achieved by giving priority to COMPASS and limiting CNGS to its basic
request. These improvements, and
especially Linac4, should allow reaching the “ultimate” luminosity presently
foreseen in the LHC by providing a proton beam with the “ultimate”
characteristics.
Table 4 Proton flux in 2010 after implementation of the improvements recommended by the HIP WG.
|
|
Estimated
flux |
Basic
user’s request |
|
|
CNGS
flux |
7.5
(4.5) |
4.5 |
1019
pot/year |
|
COMPASS
spills |
3.3
(5.6) |
7.2 |
105
/year |
|
ISOLDE
flux |
6.4 [2240] |
1.9 [1350] |
(μA)
[pulses/hour] |
|
PS East
area spills |
1.5 |
1.3 |
106
/year |
|
nToF
flux |
1.6 |
1.5 |
1019
pot/year |
4.1.2
Long
term possibilities
Decisions for the
long term (beyond 2010) have to take into account (i) the need to replace the
aging accelerators, (ii) the plans for upgrading the LHC and (iii) the future
physics programmes. Some scenarios have already been proposed for the LHC
upgrade, and, for example, the interest of a new 1 TeV injector replacing
the SPS has been mentioned [Bruning02] which would probably have to be coupled
with a new 50 GeV synchrotron replacing the PS. However, a detailed study
is still needed to compare the different possibilities and draw all
conclusions.
Concerning the
future physics programmes, the HIP working group has already identified a number
of possibilities envisaged by nuclear and neutrino physicists that could be
satisfied with a multi-MW/ few GeV proton driver like the SPL. Since then,
requests for physics with kaons and muons have shown the potential interest of a
multi-MW proton source at 30-50 GeV. Although, in principle, all these
requirements can be simultaneously satisfied, the needed resources are rather
large and the consequences so important for the complex that priorities have to
be established, at least to plan for a staged realization.
Assuming that
accelerators are replaced not only to improve reliability but also the
characteristics of the beam (energy, intensity, brightness…), the replacement of
a given machine should be coupled with the change of its injector(s). Therefore
the decision process begins at the low energy end and progressively covers all
the energy range. The possibilities and the benefits for the different families
of users are shown in Table
5. The comments and numbers are indicative and subject
to evolution. The various schemes will require further and detailed studies
before realistic proposals can be made.
Table 5 Possible improvement to the
accelerator complex
(“RCS”=Rapid Cycling Synchrotron, “HEP”=High Energy Physics, “mMW”=multi-MW, “SC”=Superconducting)
|
Present
accelerator |
Replacement
accelerator |
Improvement |
INTEREST
FOR | |||
|
LHC
upgrade |
Neutrino physics beyond
CNGS |
Radio-active ion beams
beyond ISOLDE |
Physics with kaons and
muons | |||
|
Linac2 |
Linac4 |
50
®
160
MeV H+
® H- |
+ |
0 (if
alone) |
0 (if
alone) |
0 (if
alone) |
|
PSB |
2.2 GeV RCS for
HEP |
1.4 ® 2.2
GeV 10 ® 250
kW Brightness ´
2 |
+ |
0 (if
alone) |
+ |
0 (if
alone) |
|
2.2 GeV/mMW
RCS |
1.4 ® 2.2
GeV 0.01 ® 4
MW Brightness ´
2 |
+ |
+++ for super-beam and
beta-beam |
+ (too short beam
pulse) |
0 (if
alone) | |
|
2.2 GeV/50
Hz SPL |
1.4 ® 2.2
GeV 0.01 ® 4
MW Brightness ´
2 |
+ |
+++ for super-beam and
beta-beam |
+++ |
0 (if
alone) | |
|
PS |
50 GeV SC PS for
HEP |
26 ® 50
GeV Intensity ´
2 Brightness ´
2 |
++ |
0 (if
alone) |
0 |
+ |
|
50 GeV/5 Hz
RCS |
26 ® 50
GeV 0.1 ® 4
MW Brightness ´
2 |
++ |
++ |
0 |
+++ | |
|
SPS |
1 TeV SC
Synchrotron |
0.45 ® 1
TeV Intensity ´
2 Brightness ´
2 |
+++ |
? |
0 |
+++ |
Linac2
Linac4 is a
necessary first step, whatever the choices for the other machines, because it is
designed to be compatible with the most demanding applications. For the higher
energy accelerators, the choice is more open and depends upon the physics
programmes.
PSB
If a second
generation ISOL-type facility has to be hosted at CERN, the SPL is the ideal
solution, which can also be used for all scenarios of neutrino physics
(super-beam, beta-beam and neutrino factory). The SPL would also be an
outstanding replacement of the PSB for the following accelerators serving high
energy physics experiments. Once the precise goals of such a multi-MW/ few GeV
driver are defined, the possibility of an RCS-based solution should be analysed
and compared with the SPL.
If no experimental
programme is approved that needs such a beam power at a few GeV, the most
economical solution is to build a small size RCS able to fill the PS or its
successor in 4 or 8 pulses. Most beam pulses would be available for other users,
which could be of interest for radio-active ion production, although not at the
level required by EURISOL (~ 200 kW of beam power instead of 4 MW) [Eurisol_web].
PS
The low energy of
the PS beam presently limits the SPS performance and the situation will be worse
if the SPS is replaced with a superconducting synchrotron reaching 1 TeV.
The present estimate is that the successor of the PS should deliver beam at
approximately 50 GeV. If a multi-MW beam power is needed at that energy, a Rapid
Cycling Synchrotron has to be considered. It would be a very challenging
machine, surpassing the most ambitious synchrotron presently in construction in
Japan [Jparc_web]. Moreover, it would probably lack the flexibility of the
present PS which would then have to be maintained in operation for the needs of
heavy ions for LHC and slow ejection to the East area.
If multi-MW of beam
power at 50 GeV is not needed, a synchrotron using superconducting magnets could
replace the PS. The key technological item for such a synchrotron will be a fast
pulsing superconducting dipole reaching a field of 4 to 6 Tesla in 2 to 3
seconds. The magnets in development for the needs of SIS100 at GSI would be of
interest for that application [Fair]. The new process of multi-turn ejection
which minimizes beam loss should be used.
SPS
Injection at 1 TeV
in the LHC would drastically ease operation with the present magnets, open some
interesting possibilities for upgrading the luminosity beyond the ultimate
value, and would even be necessary for an energy upgrade [Bruning02]. Other
users could also be interested, provided the new machine is capable of slow
ejection. The developments taking place in GSI for the superconducting magnets
of SIS300 could be exploited [Fair].
LHC
Extracted proton
beams at 7 TeV are a potential field of investigation. The physics case should
however be properly analysed.
4.2 The Superconducting Proton Linac (SPL) and its potential
(R. Garoby, W.
Scandale)
4.2.1
Description
The SPL is a
multi-GeV, multi-MW (typically 2.2 GeV/4 MW) linear proton accelerator. The basic characteristics of the first
Conceptual Design [Spl_web], [Vretenar00] are summarized in Table
6. Operating at 50 Hz, it will be used both as a
high-performance injector for the PS, replacing the PSB, and as a high-power
proton driver for other physics applications, possibly complemented with an
accumulator and a compressor rings.
Table 6 Main SPL parameters (CDR 1)
|
Type
of ion |
H- |
|
|
Kinetic
energy |
2.2 |
GeV |
|
Mean
current during the pulse |
13 |
mA |
|
Beam
duty cycle |
14.0 |
% |
|
Mean
beam power |
4 |
MW |
|
Pulse
frequency |
50 |
Hz |
|
Pulse
duration |
2.80 |
ms |
|
Number
of H-
per pulse |
2.27 |
´
1014 |
|
Bunch
frequency |
352.2 |
MHz |
|
Chopping
duty cycle |
61.6 |
% |
|
Successive
bunches/No. of buckets |
5/8 |
|
|
Norm.
r.m.s. transverse emittance |
0.4 |
p
mm mrad |
|
Longitudinal
r.m.s. emittance |
0.3 |
p
deg MeV |
The low energy part, up to 160 MeV kinetic
energy, is equipped with room temperature accelerating structures and makes
extensive use of LEP RF equipment at 352 MHz. It is called Linac4 because
it is proposed to be first employed to replace the present Linac2 [Garoby04].
Its characteristics in both modes of operation are outlined in Table 6.
In the initial
design of the SPL, based on the quasi-exclusive use of LEP RF hardware,
acceleration beyond 160 MeV took place in a 550 m long superconducting
linac section which brought the beam kinetic energy up to 2.2 GeV. The schematic
layout of this version of the SPL is presented in Figure
24 A second
Conceptual Design is in preparation and will be published in 2005. It will take
into account the results from the HARP experiments and the outcome of recent
developments in superconducting RF. Instead of the 352 MHz LEP cavities,
new bulk Niobium cavities will be used at 704 MHz. For the same beam power and
cost, the machine will be more compact or, if a higher energy is necessary, it
could fit inside the same footprint.
Table 7 Linac 4
specifications.
|
|
Phase
1 (PSB) |
Phase
2 (SPL) |
|
|
Maximum
repetition rate |
2 |
50 |
Hz |
|
Source
current |
50 |
30 |
mA |
|
RFQ
current |
40 |
21 |
mA |
|
Chopper
beam-on factor |
75 |
62 |
% |
|
Current
after chopper |
30 |
13 |
mA |
|
Pulse
length (max.) |
0.5 |
2.8 |
ms |
|
Average
current |
15 |
1820 |
mA |
|
Max.
beam duty cycle |
0.1 |
14 |
% |
|
Number
of particles per pulse |
0.9 |
2.3 |
´
1014 |
|
Transv.
emittance (rms, norm.) |
0.28 |
0.28 |
p mm mrad |
|
Longitudinal
emittance (rms) |
0.15 |
0.15 |
p
deg MeV |
Figure 24 : SPL schematic layout (CDR 1 design for the superconducting part).
4.2.2
Applications
The
SPL is ideal as a proton driver for a second generation ISOL facility
(“EURISOL”) [Eurisol_web] and for all scenarios of neutrino physics (super-beam,
beta-beam and neutrino factory) [Muons_web]. It would also be a top class
replacement for the PSB. For the superbeam option an accumulator ring is needed
to shorten the beam pulse from 2.8 ms to 3 ms.
For a neutrino factory, a second synchrotron has to be built to reduce bunch
length to 1 ns rms. In the proposed layout on the Meyrin site, these rings
are placed inside the ISR building and connection with the existing machines
re-uses existing tunnels (Figure
25).
Figure 25 : Proton driver complex on the CERN site.
4.2.3
Other
benefits
With the SPL replacing the PSB, the LHC will benefit from:
- the increased brightness of the PS beam that will be welcome for the luminosity upgrade (the space charge limit in the PS is raised to the equivalent of 4´1011 protons per LHC bunch within the nominal emittances).
- an extended flexibility in the choice of bunch spacing,
- the simplification of the LHC filling scheme and the “comfortable” performance margin that should increase reliability and integrated luminosity.
Limited profit is expected in terms of intensity per pulse from the PS and SPS, because these machines will already be close to their ultimate capabilities after the installation of linac4.
Most of the SPL being superconducting, it is conceivable to lengthen the beam pulse and increase the beam power by upgrading the electrical and cooling infrastructure. If necessary more high power users could then be accommodated.
4.2.4
Planning
In a context of renovation of the injector complex, it makes sense to begin with the low accelerators because (i) the low energy machines are the oldest, (ii) beam brighness is defined at low energy and (iii) the following accelerators can be based on a high performance/state of the art injector. The choice of the future machine that will replace the PSB has to be made early.
The
realization of the SPL is split in three phases, in increasing
order of beam energy, cost and benefits. An indicative planning highlighting the
key dates is given in Fig. 3.3.
In the first
phase the performance of the pre-injector, up to 3 MeV of kinetic energy, will
be investigated. A test stand equipped with an RFQ accelerator has been funded
and is presently under preparation, with the goal of operating with beam during
the year 2007.
In the second
phase, Linac4 will be built to replace Linac2, and increase by a factor of two
the intensity and brightness of the PSB beam. Linac4 is a useful first step, whatever the
choices for the other machines, because it is designed to be compatible with the
most demanding applications. Developments for Linac4 [Hippi_web] are taking
place with the support of the European Union and of the International Science
and Technology Center (Moscow). CERN management confirmed recently its
commitment to decide in 2006, with construction starting in 2007. The
setting-up with beam could then take place in 2010 and operation for physics
could begin in 2011 with immediate benefits for LHC and ISOLDE.
Figure 26: Indicative multi-year planning for the full SPL project.
In the third phase, the
full SPL would be built. The decision on its construction will depend upon the
future physics programmes at CERN and upon the needs of the LHC upgrade.
Considering that finalization and setting-up of the SPL imply interruption of
the proton beams for one year, it is logical to plan it during the shutdown for
LHC upgrade which is estimated to be in 2014. To match this date, the decision
of construction has to be made in 2008.
4.3
The Rapid Cycling Synchrotron
options
(C.
Prior)
Two criteria have
been identified and generally accepted as essential to the definition of the
type of machine known as a proton driver:
C1:
the need for high
beam power, usually within the range 1 to 4MW, possibly achieved via a phased
upgrade scheme;
C2:
for the neutrino factory application, the ability to
produce high intensity short bunches of protons, with a representative time
duration of 1–2 ns (rms). For a neutrino superbeam, a pulsed beam with a duty
factor of 10-4 is sufficient.
To
put these requirements in context, it is useful to consider the list of existing
and proposed proton sources shown in Table
8 and see the extent to which they meet the criteria C1
and C2. The most powerful pulsed machines in operation output approximately
0.15MW and those at the construction phase are generally aimed at £
1MW, with peak power expected to be reached after several years of progressive
commissioning and development. Furthermore, not all of these will satisfy the
criterion C2 easily. The step to ³4MW
should not be under-estimated, and meeting full proton driver specifications
will be an extremely challenging task.
Table 8 Parameters of
Existing and Proposed Proton Sources
4.3.1
ISIS
Of the machines
listed in Table 1, ISIS at the Rutherford Appleton Laboratory (RAL) is the
world’s most powerful source of pulsed neutrons and is approaching almost 20
years of successful operation. The accelerating system comprises a 70MeV
H-
linac injecting via
an Al2O3
stripping foil into
an 800MeV proton synchrotron. Each pulse consists of two bunches of
approximately 100 ns duration, directed onto a tantalum target at a repetition
rate of 50 Hz, where a variety of experiments are carried out for condensed
matter research.
Although far below
the levels of performance required in a proton driver, several special features
have nevertheless been built into the ISIS accelerators and are of importance
for next-generation designs. Injection of H-
is essential in order
to build up the required beam intensity within an acceptable transverse
emittance. To keep stripping foil temperatures to reasonable levels, phase space
painting is included via vertical orbit beam bumps, and to trap and accelerate
as many protons as possible, the total RF voltage in the synchrotron is varied
according to a prescribed programme during the cycle.
Dampig of the head-tail instability can be done by
changing the vertical tune during injection, and, indeed, variable tune
throughout the cycle is an important feature of ISIS and all high intensity
machines. Of more interest is the synchrotron’s resistance to the e-p
instability thought to be caused by the so-called electron cloud phenomenon. At
high intensities, protons can interact with residual gas to release electrons
which are first trapped within the bunch and then released from the tail to hit
the vacuum chamber walls. Secondary electrons are released that can in turn
interact with successive proton bunches, possibly producing a cascade effect
leading to severe beam loss. Such behaviour is believed to limit intensity in
the Los Alamos Proton Storage Ring (PSR). The absence of any such problem at
ISIS is now thought to be due to RF shields built into the dipoles and
quadrupoles, which effectively suppress the secondary emission [Bellodi04] .
However, this conclusion is still speculative and an intensive R&D programme
is in progress to resolve the issue.
Even without the e-p
instability, ISIS still shows a loss of about 10% of the beam, generally below
80 MeV, and the bunches of 100 ns duration, while suitable for neutron
production, cannot easily be compressed to the 1 ns levels required for a
neutrino factory . A phased upgrade
path to a full proton driver is however under study and is described in
§4.3.
4.3.2
SNS and
ESS
Many of the ISIS
features were incorporated in the design for the European Spallation Source
(ESS), which in turn provided a template for the US neutron source SNS. The ESS
remains a paper study [ESS03] while
the SNS is currently under construction at Oak Ridge, Tennessee. Both have full
energy linacs feeding into accumulator rings, producing pulses of the order of 1
µs at their
spallation targets. The ESS design also includes a 2 ms long-pulse option.
However, both have had to confront the need for a very low loss system, high
beam power and high intensity achieved through charge exchange injection and
proton accumulation. Elaborate collimation systems are incorporated into the
linacs and rings. Special features have been included, such as fast beam
choppers in the linacs at energies of 2–3MeV and achromatic arcs in the transfer
lines from the linacs to the rings, to facilitate low loss H-
injection. Phase space painting during injection is used
in both cases, with the ESS also carrying out energy ramping in the linac-ring
transfer line and ring RF steering during accumulation. The ESS design also
attempts to reduce problems caused by high intensity by splitting the protons
between two rings stacked on top of one another.
Neither ESS nor SNS
conforms to the strict definition of a proton driver, however. Although both
meet the high beam power criterion, bunch compression could only be achieved
through the use of an additional ring, where several megavolts of RF would be
required.
The enterprising
J-PARC project currently under construction at Tokai-mura in Japan, is the first
proton driver proper to be built, albeit at the lower end of the beam power
range (see Table 1). Based on rapid cycling synchrotrons (RCS), the complex
contains a 3 GeV ring producing proton pulses for spallation neutrons and a
50GeV ring in which bunch compression may be carried out. A dedicated neutrino
factory is being planned with muons, generated from a pion target by the proton
driver, being accelerated in a series of fixed-field, alternating gradient
(FFAG) rings before decaying to neutrinos in a dedicated storage ring. Further
details and a status report of this project are given in chapter 3.1.
4.3.3
Ideas for RCS-based
Proton Drivers
Whether the scenario
adopted is a full energy linac with accumulator ring (such as SNS) or a
synchrotron-based system (such as ISIS or J-PARC), the lessons that have been
learnt from the last ten years of study can be summarized as follows:
• To achieve a beam
power of several megawatts requires a careful balance of repetition frequency
and energy
• Building up the
intensity in the ring through H- charge exchange injection is a demanding task.
Stripping foil temperatures must be controlled and beam dumps are required for
unstripped H- and partially stripped H0 ions. Studies for the ESS
suggest that a suitable choice of the injection beam energy can minimise
problems arising from different H0 excited states [ESS03] . Injection
conditions (including orbit bumps, RF voltages and optical Twiss parameters)
must be chosen to maintain uncontrolled beam losses below the accepted level of
0.01%. The transverse distribution of the accumulated beam must be as uniform as
possible to avoid high peak current and consequential space charge
problems.
• The separate
operations of compressing the proton bunches to nanosecond (rms) durations and
particle accumulation impose entirely different demands on the lattice beam
optics. To devise a system which can meet both requirements is extremely
diffcult. The CERN solution is to use a separate compressor ring, based on a
simple FODO lattice, in which the accumulated bunches circulate for only ~7
revolutions while being compressed by a total of about 8MV of RF voltage. RCS
scenarios attempt to balance the operations of accumulation, acceleration and
compression more evenly between systems of rings, and the peak RF requirements
can generally be kept lower.
• At such high levels
of longitudinal bunch compression, the beam current is high (~1000 A). Space
charge will affct the lattice parameters (b-functions, tune,
transition energy) and the non-linear optical behaviour needs to be carefully
studied.
• Bunch compression
is facilitated if the original longitudinal emittance is small. Injection at a
lower energy might be preferable for such machines.
4.3.4
Design
models
Models developed at
the Rutherford Appleton Laboratory extend these ideas. A linac accelerating
H-
ions to an energy in
the range 150–200MeV provides a suitable combination of parameters to accumulate
bunches with a (normalised) longitudinal emittance of about 1 eV.s in a
compressor ring. Acceleration to top energy can then be divided between two
synchrotrons, the first with a lattice optimised for injection and low-loss
particle accumulation and the second designed for final bunch compression before
transfer to the target. The RAL designs show a method of doubling mean radii and
halving frequencies that reduces the demands on fast cycling dipole magnets and
eases the burden on the high gradient RF accelerating cavities.
The models all have a
common linac developed from designs originally formulated for the ESS [ESS03] .
Through an experimental programme at RAL, positive steps have been taken to
devise a high current (50–60 mA) H-
ion source with a
lifetime of approximately 10 weeks or longer. This is based on the ISIS Penning
source and, after extensive research with the aid of EU support, is probably the
best of its kind available today. From the ion source the beam is matched by the
Low Energy Beam Transport system (LEBT) into a radio frequency quadrupole (RFQ),
bunched and accelerated to 2.5 MeV. The fast beam chopper [Cla02] which follows is a crucial component of
the structure, without which low-loss ring accumulation would be impossible. As
the frequency of the RFQ is likely to be 234.8MHz, the gap between micro-pulses
is of the order of 2–3 ns during which a kicker field has to rise to deflect up
to 30% of the micro-pulse train to a beam dump. Operation is at an harmonic
multiple of the ring revolution frequency. An intensive R&D programme has
been set up aimed at full beam tests within five years (finances permitting).
Some support has been obtained from the EU within the Framework Programme 6
(FP6) and the merits of the RAL chopper design will be compared with an
alternative model under study at CERN.
Beam passing through
the chopper is accelerated in a drift tube linac (DTL) to an energy of 90MeV and
undergoes a triple frequency jump to 704.4MHz before being raised to 180MeV in a
side-coupled linac (SCL) [Gerigk04] . This work also receives funding from the
EU under FP6.
4.3.5
5 GeV, 4MW
Model
The HARP experiment
(see chapter 5.2.2) will indicate the optimum driver energy for maximum
pion yield for a neutrino factory. Pending the results, models covering a range
of energies have been developed.
The first (Figure 27) has a top energy of 5 GeV and is site-independent.
The synchrotron system consists of two stacked booster rings of mean radius
32.5m each taking two bunches of 2.5
×
1013
protons to an energy
of 1.2 GeV at a frequency of 50 Hz. The injection period per ring is 0.2 ms and
the rings are filled immediately after one another. A simulation of the
injection into longitudinal phase space is shown in Figure 6. Although chopped,
the beam does not initially fit completely inside the stable phase space bucket,
but particles outside are gathered up in the non-adiabatic process as voltages
and magnetic fields change and acceleration begins. Momentum ramping and RF
steering are used to assist trapping and keep beam loss, which is mainly from
scattering in the injection foil, below 0.01%. Over 160 injection turns, the
average number of foil traversals per circulating proton is low, keeping
temperatures down and probably allowing use of an ISIS-type Al2O3
stripping foil,
though carbon, with a higher sublimation temperature, would be a safe,
alternative choice.
Figure 27 Rapid Cycling Synchrotron models at 5 GeV (left) and 15 GeV
(right)
Extraction from both
synchrotrons has to be at the same energy, which means on the upward part of the
accelerating cycle for the second ring and the downward part for the first. All
four bunches - which are 100 ns in duration - are transferred to one of the main
synchrotrons, which have twice the radius (65 m) and operate at half the
frequency, 25 Hz at harmonic number h
=
8.
The beam is
accelerated to 5 GeV over 20 ms, during which time the boosters reset and
operate again so that as the first main ring is extracted, the second main ring
is filled. Extracting alternately in this way restores the 50 Hz cycle. Bunch
compression is achieved by choosing the main ring to have g =
6.5, only
very slightly greater than g
= 6.33 at top
energy. Towards the end of acceleration, the bunches are then almost frozen
longitudinally. An additional 500 kV of RF at harmonic number h
= 24 are brought into
play and this is sufficient to compress the bunches to 1 ns (rms). The process
is accompanied by an increase in momentum spread, which requires non-linear
optics to be considered, but a sextupole scheme has been devised to compensate
for these high order effects. Further details are given in [Prior00] and [Prior00a] .
4.3.6
15 GeV, 4–6MW
Model
A 15 GeV driver has
also been designed on the same principles, with the main rings specifically of a
size to fit within the CERN ISR tunnel. The booster synchrotrons have mean
radius 50 m, h
= 3 and output 50 ns
bunches at 3 GeV and 25 Hz, after accumulation and acceleration from the 180MeV
H-
linac. The main rings
have radius 150 m, and each compresses 6 bunches to 1 ns (rms) with a peak RF
voltage of 1.7MV at harmonic number 36. Space charge tune shifts are of the
order of -0.02. Figure
27 shows a possible layout, with the boosters neatly
fitted inside the main synchrotrons. For simplicity, all but one of the transfer
lines between the rings have been suppressed. The model is nominally designed
for 4MW output but is capable of being upgraded to 6MW by increasing the number
of bunches.
4.3.7
4.1.3 30 GeV, 4MW
Model
Adapting parameters
in a different manner, a 30 GeV slow cycling synchrotron at 8 Hz has also been
designed for the ISR tunnel [Aut01] . The scenario uses the same 180MeV
H-
linac and
180
achromat described
above, and has a booster accelerating two proton bunches to 2.2 GeV at 50 Hz.
Batches of 8 bunches (1014
protons in total) are
accelerated in the main ring to 30 GeV, which requires a total of 3.8MV of peak
RF voltage for the 1 ns rms bunch compression. Such a machine would not only
provide an alternative to the CERN SPL but could also inject directly into the
CERN SPS above transition energy. It might also be considered as a possible
replacement for the elderly CERN PS.
4.3.8
ISIS
Upgrades
In its present
configuration, the machine is limited by space charge to an intensity of
2.5×1013
protons per pulse. A
combined h
= 2, h
= 4 RF system is
being installed which, by stretching the stable areas of longitudinal phase
space, may allow up to 50% more beam to be injected without any change in the
transverse tune effects [Prior93] . The relative phases beween the RF harmonics
have to be carefully controlled throughout the cycle but the general principle
is well-tried and should provide additional benefits for neutron scatterers for
a fairly modest cost. A second target station is also being built, to operate at
10Hz and, by taking one in five pulses from the existing 50 Hz target, will
effectively absorb the extra beam power.
The second phase of
the upgrade is to replace the ageing ISIS linac with the 180MeV linac described
above. At this energy, space charge levels at injection are halved, and initial
studies suggest that the synchrotron could output 0.4MW of beam power, which the
present target could probably just about withstand.
Beyond this, the only
practical method of increasing the power of the facility is by raising the
energy through the addition of a second synchrotron. Studies have been carried
out to enlarge the 8 GeV ring developed for Fermilab to a mean radius of 78m,
three times ISIS’s 26 m. This ring could then operate in two modes. Taking
ISIS’s pulses by a simple bucket-to-bucket transfer, the beam could be
accelerated to 3.5GeV to produce 100 ns bunches at an energy suitable for a
1–1.5MW, 50 Hz spallation neutron source. This is a fairly costly project since
a new target would be required. In the machine’s alternative mode, one in three
ISIS pulses could be accelerated in the main synchrotron to 8 GeV at a frequency
of 16.67 Hz (the other two pulses being directed to a beam dump). Experiments of
nanosecond bunch compression
could be carried out,
studies of lattice and beam behaviour near transition would be possible, and the
beam could provide the means for neutrino factory pion target tests. Further
development would entail the construction of a new booster, effectively
replacing the current ISIS accelerator. This could fit inside the 78m ring, thus
allowing ISIS to continue operation with relatively little disruption to users.
The booster is based on stacked 1.2 GeV, 50 Hz synchrotrons fed by the 180MeV
H-
linac via the
achromat of Figure 27. The main synchrotron, operating at 25 Hz, would be
upgraded to 2.5MW and would provide an enhanced neutron facility at 3 GeV with
further scope for neutrino factory tests at 6 or 8 GeV.
The final phase of
the upgrade programme would be to build a second main synchrotron, stacked on
top of he first, so as to recoup the overall 50 Hz frequency as explained above.
This would provide a 4–5MW proton driver in the full sense of the term and
provide a dual neutron/neutrino facility that would fit comfortably on the RAL
site.
4.3.9
Proton Driver R &
D
R&D is of course
of vital importance, and the following representative (but incomplete) list of
topics is adapted from the Snowmass working group’s report [PDWG01]
.
(1) The requirements
from the H-
ion source are a
current of 60–75 mA, 6–12% duty cycle, and a normalised rms emittance
enrms
»
0.2
p
µrad.m. The lifetime
should be at least 2 months. The RAL ISIS ion source is the only source
realistically likely to meet these demands in the immediate
future.
(2) Work is required
on radio frequency quadrupole linacs (RFQ) at frequencies in the range 200 to
400MHz with currents up to 100 mA. 99% transmission efficiency is a goal and the
unit must have its higher order modes suppressed.
(3) A fast beam
chopper is essential, with rise time<_2 ns.
Materials and configurations meeting the thermal demands imposed on the chopper
beam dump need to be studied, and a means for handling 5–10kW of beam power
should be assessed.
(4) Funnelling may be
required to double the linac current, particularly in full-energy
linac/accumulator ring systems. The ESS design contains a 20MeV funnel and there
are plans to build and test this at RAL at some future date [Prior99]
.
(5) R&D is
required for high efficiency and high reliability RF sources, such as inductive
output tubes (IOT) and multi-beam klystrons.
(6) In the area of
linac diagnostics, studies should be carried out on: (a) noninvasive
H-
beam profile
measurements, using for example laser wire, ionization and fluorescent-based
techniques; (b) on-line measurements of beam energy and energy spread; (c) halo
monitors, especially in superconducting systems; (d) longitudinal bunch shape
measurements.
(7) The EU FP6 HIPPI
contract covers work on high-gradient low and intermediate b
superconducting
cavities and spoke cavities. Much will be learnt from the SNS experience in
cryogenics.
(8) There is an
active group currently analysing space charge problems, in particular exploring
fast accurate codes and devising and carrying out benchmarking tests (see
[Prior03b] ).
(9) Experimental
studies of ring lattices are desirable, for example to explore the higher order
dependency of gt
on Dp/p, tune
shifts and space charge.
(10) Injection foil
lifetime and stripping effciency need to be investigated and experiments on the
lifetime of H0
excited states as a
function of magnetic field and beam energy should be carried out. Studies of the
efficiency of slow extraction systems would also be of
interest.
(11) There is an
active international collaboration trying to understand the electron cloud
problem. Here too codes are being developed to incorporate an increasing range
of physical effects. A benchmarking programme is under way but needs to run in
parallel with the experimental programme proposed at ISIS and ongoing studies at
the Los Alamos PSR and CERN.
(12) Ring beam loss,
collimation and radiation protection issues are of high priority. 3D code
development is required, and engineering aspects of collimation and beam dumps
should be investigated. The efficiency of beam-in-gap cleaning systems will
benefit from SNS experience. Collimation with resonant extraction could, with
interest, be explored.
(13) Diagnostics need
to be developed to measure beam parameters during ring injection, for example
beam position monitors over a large dynamic range for turn by turn measurements,
and equipment for fast, accurate, non-invasive tune
measurements.
(14) Covering a range
of different options, studies of RF in the ring could profitably be carried out
to develop: low frequency
(~5 MHz),
high gradient (~1MV/m) RF systems, some with ~50% duty cycle; (c) high voltage
(>100 kV)
barrier bucket systems; (d) transient beam loading compensation schemes (e.g.
for low-Q magnetic alloy (MA) cavities).
(15) Synchrotron
magnets with combinations of different harmonic fields need to be designed and
tested. At RAL and Fermilab, for instance, a magnetic field
variation
B(t) =
B0
-
B1
cos(2pft) +
B2
sin(4pft)
is proposed with
B2
chosen to help
minimise the peak RF voltages needed for acceleration. Suitable power supplies
need to be developed, and their cost effectiveness taken into
account.
(16) Since most
proton driver rings are likely to include inductive inserts to reduce the
effects of high space charge levels during bunch compression, a formal R&D
programme would be desirable covering aspects of both theory and practice
(programmable inserts, inserts with large inductive impedance). An experimental
programme is planned for the Fermilab Booster and the J-PARC
project.
4.3.10 Conclusions
While there is much work to be done, it appears that there are no insurmountable difficulties to the construction of a successful proton driver. By sharing the challenging aspects over different parts of a machine — chopping in the low energy part of the linac, halo control in intermediate energy stages and the achromat, acceleration and bunch compression in separate rings, and doubling the rings to reduce space charge as necessary — a synchrotron-based scenario provides a feasible and cost-effective solution for future high power needs. With the support of organisations such as the European Union through Framework 6, good progress is already being made in the design of high intensity linacs with energies up to 200MeV, and further backing will be requested for synchrotron development in the near future. A model has been devised for a slow-cycling replacement for the CERN PS, and the ISIS upgrade plans, which progressively develop an existing facility into a machine for both high energy physics and condensed matter studies, look particularly interesting.
5
Facilities around the intense proton
source
5.1 Additional installations for a neutrino physics facility
(A.
Blondel, S. Geer, H. Haseroth, A. Rubbia)
5.1.1 Overview
Several neutrino physics facilities have been discussed as shown in Figure 8. The beta-beam is quite different and will be discussed in section 5.4. The Neutrino Factory based on a muon storage ring is being investigated in the US, Japan and Europe since quite a few years. A "Neutrino Superbeam" is a conventional neutrino beam from p decay and is very similar to the front end of the Neutrino Factory. This section concentrates on what is needed behind a proton driver for a Superbeam, then a Neutrino Factory. The overall layout is repeated in Figure 28; as can be seen in Figure 29, a suitable arrangement could be found at CERN.
Figure 28 Schematic layout of a Neutrino Factory
Figure 29 Possible layout of a Neutrino Factory on the CERN site
5.1.2 The Neutrino Factory
New accelerator technologies offer
the possibility of building, not too many years in the future, an accelerator
complex to produce and capture more than 1020 muons per year. It has been proposed to build a Neutrino Factory [nufact] by
accelerating the muons from this intense source to energies of several GeV,
injecting the muons into a storage ring having long straight sections, and
exploiting the intense neutrino beams that are produced by muons decaying in the
straight sections. The decays: 
and 
offer
exciting possibilities to pursue the study of neutrino oscillations and neutrino
interactions with exquisite precision.
To
create such an intense muon source, a Neutrino Factory requires an intense
multi-GeV proton source capable of producing a primary proton beam with a beam
power of 1~MW or more on target. This is just the proton source required in the
medium term for Neutrino Superbeams. Hence, there is a natural evolution from
Superbeam experiments to Neutrino Factory experiments.
Neutrino Factory designs have been proposed in Europe [Aut99], [Gru02], the US [MuColl] [StudyI][StudyII], and Japan [Japnufact]. Of the three designs, the one in the US is the most developed, and we will use it as a example in general with a few exceptions. The Neutrino Factory consists of the following subsystems:
- Proton Driver. Provides 1-4 MW of protons on a pion production target. For the neutrino factory application the energy of the beam is not critical, since it has been shown that the production of pions is roughly proportional to beam power. In the low energy region, this statement may need to be substantiated with e.g. the Harp measurements (see section 5.2 ). The time structure of the proton beam has to be matched with the time spread induced by pion decay (1-2 ns); for a linac driver, this requires an additional accumulator and compressor ring. For the superbeam however, the energy of the protons directly impacts on the resulting neutrino beam energy from pion decay which is typically 5 to 10% of that of the incident protons.
- Target , Capture and Decay. A high-power target sits within a 20T superconducting solenoid, which captures the pions. The high magnetic field smoothly decreases to 1.75T downstream of the target, matching into a long solenoid decay channel. A design with horn collection has been proposed at CERN for the neutrino factory, with the benefit that it can be also used for a superbeam design. The advantage of the horn that it sign-selects the pions and muons is compensated by the fact that in a neutrino factory design one could contemplate to accelerate both signs of muons, thus doubling the available flux.
- Bunching and Phase Rotation. The muons from the decaying pions are bunched using a system of rf cavities with frequencies that vary along the channel. A second series of rf cavities with higher gradients is used to rotate the beam in longitudinal phase-space, reducing the energy spread of the muons.
- Cooling. A solenoid focusing channel with high-gradient 201 MHz rf cavities and either liquid-hydrogen or LiH absorbers is used to reduce the transverse phase-space occupied by the beam. The muons lose, by dE/dx losses, both longitudinal- and transverse-momentum as they pass through the absorbers. The longitudinal momentum is replaced by re-acceleration in the rf cavities.
- Acceleration. The central momentum of the muons exiting the cooling channel is 220 MeV/c. A superconducting linac with solenoid focusing is used to raise the energy to 1.5 GeV. Thereafter, a Recirculating Linear Accelerator raises the energy to 5 GeV, and a pair of Fixed-Field Alternating Gradient rings using quadrupole triplet focusing accelerate the beam to at least 20 GeV.
- Storage
Ring. A compact racetrack geometry ring is used,
in which 35% of the muons decay in the neutrino beam-forming straight section.
If both signs are accelerated, one can inject in two superimposed rings or in
two parallel straight sections.
This scheme produces over 2 ´ 1020 useful muon decays per operational year. The European Neutrino Factory design is similar in general to the US design, but differs in the technologies chosen to implement some of the subsystems. The Japanese design is very different, and uses very large acceptance accelerators rather than a system that reduces the phase-space occupied by the muons so they fit within the more limited acceptance of a more normal acceleration scheme.
5.1.3 The proton Driver
High power of the proton beam is a challenge in terms of beam losses, which can yield undesired activation of the machine components making hands-on maintenance impossible. In the CERN scheme with an H- linac with charge exchange injection into an accumulator ring the stripping foil needs very close attention. A common problem of all proton drivers is the production of very short bunches in order to reduce finally the energy spread of the muons with a scheme called “debunching” amongst linac experts (“phase rotation” for neutrino people).
5.1.4 The target
For a high power target there are many areas of application in neutrino physics, studies of rare processes initiated by muons, studies of materials with neutron beams from a spallation source, the accelerator production of tritium, accelerator transmutation of waste, accelerator test facilities for fusion reactor materials and many others.
The main problems are the survival of components against melting/vaporization, the survival of components against beam-induced pressure waves (in the case of pulsed proton beams), the survival of components against radiation damage.
Massive solid targets (or rotating-wheel targets), typically water cooled, have been used in most applications with not more than 1-MW beam power. But for beam powers in excess of 1 MW such passive solid targets become very problematic in view of the challenges mentioned above. This has led to consideration of flowing liquid targets: mercury, molten lead, molten Pb/Bi, etc.
Figure 30 Experiments with liquid mercury jets. On the left is seen a jet exposed to a beam of 4 1012 protons of 24 GeV at BNL; the jet explosion begins long enough after the impact. On the right is shown the behaviour of the jet inside a high magnetic field; the jet is able to penetrate the intense magnetic field, and Eddie currents smoothen it.
The usual liquid target systems still require solid-walled containment vessels and beam windows that isolate the target region from the rest of the accelerator complex. An example of such a design within a horn is given in Figure 31. Experience has shown that if a liquid target is confined inside a metal pipe in the region of the interaction with a pulsed proton beam, then the beam-induced pressure waves can cause pitting (associated with cavitation during the negative-pressure phases of the waves) and possible failure of the solid wall. Such concerns indicate that it would be preferable to have a flowing liquid target in the form of a free jet, at least in the region of interaction with the proton beam. In a recent workshop for "High-Power Targetry for Future Accelerators" in Ronkonkoma it was stated that Targets for 1 MW machines exist (but unproven) and that there is no convincing solution for the 4 MW class machines.
Rotating solid targets, granular targets, liquid metal targets, e.g. Hg have been considered at several labs. Tests with Hg were done at BNL and CERN. Tests with Hg jets injected into high magnetic fields were done by CERN at Grenoble. (Figure 30).
A number of valuable results were obtained, like the measurement of the radial velocity of the dispersal of the Hg jet as a function of the proton beam intensity and the observation that the Hg dispersal is largely transverse to the jet axis and that there is no visible manifestation of jet dispersal before 40 ms. At Grenoble the stabilizing effect of the jet when injected into a magnetic field was observed. There is now a proposal [target-exp] to the Isolde and nToF Committee for an experiment at CERN in the TT2a tunnel using a Hg jet with proton beam AND magnetic field supported by RAL, CERN, KEK, BNL and Princeton University, which would allow very good progress in the understanding of the basic mechanisms important for the design of multi MW targets.
5.1.5 Pion capture
For the pion capture different schemes are proposed. In the US a Solenoid with 10-20 Tesla is being considered (lifetime >>1 year), whereas at CERN the collection with magnetic horns is explored. A magnetic horn would be needed to select either positive or negative pions. Present estimates give a possible lifetime of 6 weeks. HARP results are needed to optimize the proton driver energy, the target and the collection device.
Figure 31 Possible layout of a Hg jet target and a horn. On the right, a prototype horn built at CERN [Gilardoni]
5.1.6 Cooling and phase rotation
Phase rotation in the CERN scheme is achieved with rf cavities operating at 88 MHz [Lombardi]. The American scheme [Study II] was using induction linacs. Now a 200 MHz rf capture system is being worked on. In both cases one lets the muon beam generated via the very short (1 ns rms) proton bunch spread out in the longitudinal direction and use the corresponding time-position correlation to correct the energy of the muons with a time-varying electric field. To perform cooling, the beam is sent through liquid hydrogen absorbers, reducing the transverse and longitudinal momenta. Subsequent reconstitution of the longitudinal momentum occurs with RF cavities. Basically the cooling channel is a linear accelerator with (liquid hydrogen) absorbers. The cooling channel will be fairly long and expensive, hence the interest in “ring coolers”, where cooling is done over many revolutions.
Ionization cooling involves many new technologies, in particular operation of high gradient RF cavities in high magnetic field, and in the vicinity of hydrogen absorbers. In order to assert the performance that can be achieved in a real channel, the MICE experiment (Figure 32) is being prepared at the RAL (UK). Liquid hydrogen absorber prototypes have been already operated at Fermilab and the first 200 MHz cavities with Be windows is being built in Berkeley, while prototypes of the tracker and detectors are operated in UK, Japan Italy and CERN [MICE].
Figure 32 Layout of the MICE experiment.
5.1.7 Acceleration
The acceleration of muons should proceed in several steps and be very fast. After an initial linear accelerator "Recirculating Linear Accelerators" (RLAs) are investigated, as normal synchrotrons are too slow and the decay losses of muons would not be tolerable (the muon’s life time is only 2.2 ms). RLAs are a good compromise between cost and speed. For the acceleration 200 MHz sc cavities, sputtered at CERN, are tested at Cornell.
Another interesting proposal might be mentioned here: the possible use of a rapidly pulsed synchrotron, which seems feasible by making use of the fairly low repetition rate, at least in the US scheme.
The use of FFAGs is also being investigated, after the successful operation of proton FFAGs in Japan. These machines have a large acceptance, both in longitudinal and transverse phase space, hence cooling may not be needed and the acceleration can be fast due to fixed magnetic field. [Keil04]
5.1.8 Decay ring
The decay ring has long straight sections to
produce the well directed neutrino beams. The geometry is quite flexible, but in
order to achieve high precision on the flux it is best to use a race-track or
triangle geometry to ensure muon precession. This allows measurement of the beam
energy and energy spread with great precision and ensures that the average
polarization is zero. The optics can be designed in such a way as to ensure a
beam divergence of less than 0.2/g, and the necessary
diagnostics (at least a beam current monitor, a polarimeter and a measurement of
beam angular divergence) can be accommodated. [Keil00],
[ECFAreport].
5.1.9 Muon Colliders
Some time ago regarded by some people as science fiction, it must be noted that the advances in cooling theory and technology are so impressive as to consider this type of machine as a real possibility in the future opening the "High Energy Frontier" to leptons.
5.1.10 Progress on Neutrino Factory design
An impressive Neutrino Factory
R&D effort has been ongoing in Europe, Japan, and the U.S. over the last few
years, and significant progress has been made towards optimizing the design,
developing and testing the required accelerator components, and significantly
reducing the cost. To illustrate progress in cost reduction, the cost estimate
for a recent update of the US design [APS04] is compared in Table 9 with the corresponding cost for the previous “Study
II” US design [Study II]. It should be noted that the Study II design cost was
based on a significant amount of engineering input to ensure design feasibility
and establish a good cost basis. This engineering step has not yet been done for
the updated design, but the new cost estimate is based on experience from the
Study II work. The conclusion is that the latest design ideas are expected to
lead to very significant cost reductions, although more work must be done to
establish a reliable new cost estimate.
Neutrino Factory R&D has
reached a critical stage in which support is required for two key international
experiments (MICE and Targetry) and a third-generation international design
study. If this support is forthcoming, a Neutrino Factory could be added to the
Neutrino Physics roadmap in less than a decade.
Table 9 Comparison of unloaded Neutrino Factory costs estimates for the US Study II design and for the latest updated US design. Costs are shown including or not including the Proton Driver and Target station in the estimates. The New design cost estimate has not yet benefited from the level of engineering effort included in the Study II work. Table from Ref. [APS04].
|
|
All (M$) |
No
Proton Driver (M$) |
No
Proton Driver & No
Target station
(M$) |
|
Study
II |
1832 |
1641 |
1538 |
|
New
/ Study II (%) |
67 |
63 |
60 |
The scientific case for pursuing Neutrino Factory R&D is strong. The encouraging technical progress in Neutrino Factory R&D over the last few years has been matched by progress in building the level of international collaboration needed for the next step, and preparing proposals for the critical R&D experiments. All of this has been accomplished with very limited funding. The next steps require an increase in funding, but to a level which is still modest considering the nature of the enterprise. If a Neutrino Factory is to remain a viable option for the future it is important that MICE, the Targetry experiment, and a third-generation international design study are supported. If this is the case, we have much to look forward to.
5.2 Hadro-production experiments
(M. Apollonio, A. Blondel)
5.2.1 Introduction
The construction of a neutrino factory or a
superbeam requires optimisation of target material, collection scheme and proton energy.
Present studies are based on simulation codes for pion production which show
large discrepancies, both in p/K yield and
(pL,pT) distributions. This reflects the poor experimental
data, based on old experiments covering small acceptances, few materials and few
incident proton energies, and the lack of a good phenomenological description
of low energy hadronic
interactions. The situation calls for a new generation of dedicated hadronic
experiments as integral part of the neutrino physics programme. The E910 experiment at BNl took data in
the late 1990’s for proton energies between 6 and 24 GeV and first results were
presented recently [BNL91004]. The MIPP experiment at Fermilab [MIPP] is
presently being commissioned for proton energies between 15 and 125 GeV. The
HARP experiment at CERN is the only one to cover the low energy range of the
baseline SPL option (protons of 2.2 GeV kinetic energy (~3 GeV/c momentum) [Vretenar00] where it is
crucial to understand the p+/p- ratio as well as the rate of K± and K0 production.
5.2.2
The HARP experiment
HARP [HARP-proposal] was proposed in 1999 as a hadro-production experiment whose goals are:
· The optimisation of the p+(p-) yield in view of a neutrino factory or a superbeam
· The calculation of beam fluxes for other experiments, K2K [K2K03] and MiniBooNE [MiniBoone]
· The improvement of the present knowledge about atmospheric neutrino fluxes
· The input for hadronic Monte Carlo generators
The first and second points will be developed in the following.
Figure 33 shows a layout of HARP; the experiment, located in
the PS T9 East Hall at CERN, collected about 420 million events in 2001-2002,
with a distribution of beam particle and energy and targets shown in Table 10 at a high DAQ rate (2.5 kHz, ~106
events/day). The detector can be ideally decomposed into a Large Angle Region
(covered by a TPC and several RPCs inside a 0.7 T solenoidal magnetic field) and
a Forward Region (covered by a spectrometer and a series of detectors for
particle identification).
Table 10 Summary of the HARP data taking campaign (2001-2002). Many materials have been tested ranging from H to Pb, at proton momenta covering an entire decade (1.5 to 15 GeV/c). Some special targets (like the K2K and MiniBooNE replicas and cryogenic targets) have been thoroughly studied.
5.2.3 Optimisation of the neutrino factory (and super-beam): large angle
The aim is to reach a precision of 5% in the pion yield (and p+/p- ratio). It should be stressed that such measurements will be also extremely useful for a super-beam. At all energies most of the pions are produced at high angles but this is especially true for the low enery of SPL. For this reason the use of Large Angle Detectors (TPC and RPCs) are of paramount importance. Presently the TPC calibration and correction of various distortions and cross-talk is underway. A campaign of calibrations using cosmic rays, radioactive sources (83Kr and 55Fe) and data was pursued [HARP03]. This calibration program allowed:
· The equalisation of gains and mapping of dead pads
· A first evaluation of the correction for cross talk in the readout planes
· The first determination of the dE/dX as a function of p
· An improvement in pT resolution
Some of these results
are summarized in fig. 2 and fig. 3 (left and right). These results will be
verified using the well-known elastic scattering processes of protons (pions) on
hydrogen target at low momenta (3 GeV/c).
Figure 34 Transversal momentum resolution as a function of pT, as measured by the TPC.
Figure 35 (left) dE/dX as a function of p, showing different particle populations (p,m and protons); (right) energy peaks for the radioactive sources used to calibrate the detector: (a) overall picture with 55Fe and 83Kr. (b) Fe peaks (at 5.9 and 3.0 keV) and Kr peaks (the main one being at 41.6 keV). This case is obtained using equalised pads.
5.2.4 The K2K and MiniBoone case: the forward analysis
This important physics case has been chosen as the subject of our first analysis. In the K2K experiment [K2K03], one of the largest systematics in the n oscillation parameters comes from the uncertainty on the far/near ratio, which depends on the p-production model used. The pion flux from KEK can be monitored and checked against simulation of the beam down to neutrino energies of 1 GeV, while for lower energies there is no experimental information. Unfortunately the oscillation effect that K2K is meant to measure takes place somewhere between 0.5 and 0.75 GeV. This translates into a (p,q) distribution for parent pions which is well covered by the HARP forward detectors (see fig. 4).
Figure 36 (p,q) distribution for pions in
the K2K case as described in the text. The parameter space is well within the
reach of the forward HARP detectors.
Figure 37 (left) momentum distribution, integrated over q, for secondary pions from
12.9 GeV/c protons impinging onto a 5% l Al target. (right) angle
distribution, integrated over p, for the same sample. Vertical axis is in
arbitrary units [Cervera04].
A special program with an Al K2K replica target has been followed by HARP; at present the collaboration is strongly focussing into this subject, aiming at the calculation of the pion cross section in a range of momenta pp<8 GeV/c and of emission angles qp<300 mrad.
Preliminary results of this analysis, based on an Al thin target at 12.9 GeV/c, have been already made public [Cervera04], and are summarized in Figure 37, in the form of shape distributions for p and q. Albeit still missing of a real determination for the systematic error they represent our first measurement of the pion yield as a function of momentum and emission angle.
5.2.5
Conclusions
The optimization of
future neutrino facilities requires good understanding of pion production by various beams and
targets. The HARP experiment was assembled very rapidly and took an extensive
data set. The experiment and its analysis require great care, but the experiment
should be able to fulfill its goals. The measurement on pion and kaon yields at
the low energy of SPL will be important for the decision on this
accelerator.
5.3 EURISOL : a new nuclear physics facility
(Y.
Blumenfeld, P.
Butler, A. Müller)
During the past two decades, progress in nuclear physics has been largely fuelled by the development and improvement of radioactive ion beams. The two main methods used to produce such beams are called projectile fragmentation and ISOL. In the former a high energy heavy ion beam impinges on a thin target and a large array of fragments is produced. The isotopes of interest are selected by a fragment separator and the resulting beam transported to the experimental areas. This method, used at GANIL, GSI, the NSCL/MSU and RIKEN, is particularly efficient for a large variety of species with short lifetimes and delivers high energy beams with relatively modest resolution qualities. The ISOL method, in use at CERN/REX-ISOLDE, GANIL/SPIRAL and TRIUMF, uses a driver accelerator (p, d or heavy ions) and a thick target. The nuclei are produced at rest, diffuse and effuse out of the target before being ionised and then accelerated in a post-accelerator. Beams of high quality but modest energy are produced. The efficiency of such a system depends on the diffusion and effusion times and certain elements, such as the refractory elements, are particularly difficult to produce due to their chemical properties.
Technologies are now being developed, which
should allow for improvements of orders of magnitude of the intensities of
radioactive beams. A vast physics program has been identified, which is
extensively discussed in other talks of this workshop. This led NuPECC to propose the construction of two ‘next
generation’ RIB infrastructures in Europe, i.e. one ISOL and one in-flight
facility. The in-flight machine would arise from a major upgrade of the current
GSI facility, while EURISOL would constitute the new ISOL
facility.
An RTD
program, for a preliminary design study of EURISOL, was coordinated by GANIL and
J. Vervier, and implemented under the auspices of the EU 5th
framework program. The result is a preliminary design report [EURISOL] which
outlines a concept for a future EURISOL facility (fig. 1). The driver
accelerator would be a super-conducting CW proton LINAC, of energy 1 GeV and
power 5 MW, with additional capability of accelerating deuterons and possibly
heavier ions with A/Q = 2. Several target stations would be built, including a
fission target with a liquid mercury converter allowing for the use of the full
5 MW beam power, and targets receiving directly the approximately 100 KW of
proton beam for production of lighter or neutron deficient isotopes. The post
accelerator would be a super-conducting heavy-ion LINAC with a maximum energy of
100 MeV/nucleon. The maximum energy is somewhat arbitrary and for a linac is
defined by cost; higher energies could be achieved at CERN by exploiting its
existing synchrotron accelerator chain or new accelerators required for the
beta-beam facility.
In
EURISOL there will be several experimental areas devoted to physics at different
energies: fundamental physics, nuclear astrophysics, nuclear structure and
nuclear reaction studies. Among the experimental equipment necessary, one can
cite ion traps and high precision spectroscopy set ups for very low energy beams
(similar to present ISOLDE equipment); a variety of high resolution and/or large
acceptance magnetic spectrometers; an innovative gamma-ray tracking array (i.e.
the AGATA concept); high granularity charged particle and neutron detectors, a
4P charged fragment detector, and a
fragment separator for production of nuclei very far from stability through
secondary fragmentation.
With the wide diversity of scientific
disciplines and individual experiments being served by the facility, various
multi-user installations (such as at the present ISOLDE) are needed, requiring
the design of a beam
switchyard that allows parallel operation.
Typical
intensities in particles per second would be 1013 for
132Sn, 1011 56Ni, 5 1013
6He, and 5 1012
for 18Ne.The total cost of such a facility was estimated at
600 M€, including buildings but excluding manpower. The large production of
6He and 18Ne would make EURISOL an attractive source of
unstable nuclei for a b-beam installation, as outlined in chapter
5.4.
Figure 38 : Conceptual layout of the EURISOL facility.
The
roadmap towards EURISOL includes three main aspects:
--The vigorous scientific exploitation of current ISOL facilities : EXCYT, Louvain, REX/ISOLDE, SPIRAL
--The construction of intermediate
generation facilities : MAFF, REX upgrade, SPES, SPIRAL2
--The design and prototyping of the
most specific and challenging parts of EURISOL in the framework of the Eurisol
design study (EURISOL_DS) proposed in the sixth framework
program.
In close
contact with the nuclear physics and neutrino communities, a design study proposal
(EURISOL_DS) was submitted in March 2004, with the aim of performing
detailed engineering
oriented studies and technical prototyping work for the future EURISOL facility,
which would be coordinated by GANIL and G. Fortuna. This design study proposal
includes 21 participating institutions from 14 European countries, as well as 21
other contributing laboratories from Europe, North America and Asia who will
provide their expertise on specific technical points. The total cost of the design study
would be 33 M€, of which 9.16 M€ is requested from the EU, the remainder being
provided by the participating institutions.
The work is to be subdivided in 11 tasks (the laboratories leading the tasks are indicated in parentheses) grouped under 4 topical subjects. Several of these tasks include a large effort of technical prototyping as specified:
•Physics, beam intensity and
safety
–Physics and instrumentation
(Liverpool)
–Beam intensity calculations
(GSI)
–Safety and radioprotection
(Saclay)
•Accelerators
:
–Proton
accelerator design (INFN Legnaro)
–Heavy ion accelerator design
(GANIL)
–SC cavity development (IPN
Orsay): prototyping of SC cavities and multipurpose
cryomodule
•Targets and ion sources :
–Multi-MW target station
(CERN) : prototyping of mercury converter
–Direct target (CERN) :
Several target-ion source prototypes
–Fission target (INFN
Legnaro) : prototyping of UCx
target
•Beam properties :
–Beam preparation (Jyväskylä)
: prototyping of 60 GHz ECR source
–Beta-beam aspects
(CERN)
Several synergies have been identified, in particular with the HIPPI JRA and the BENE network of the CARE Integrated Infrastructure Initiative. This workshop has represented an excellent opportunity to start implementing these synergies.
EURISOL, FAIR and RIA
As outlined in 3.3, the other major “next generation” nuclear facility
in Europe, FAIR, will embrace research programmes in hadron and nuclear physics,
atomic and plasma physics that are complementary to EURISOL, using intense beams
of heavy-ions and anti-protons. In the overlapping area of radioactive ion beam
physics EURISOL and FAIR will provide secondary beams in different domains of
energy and beam quality, and therefore offer different experimental conditions.
The
EURISOL facility provides very high secondary-beam intensities for many species
and beam properties (continuously variable beam energy of good definition, high
purity and small emittance), which are well adapted to highly elaborate
experimental approaches. EURISOL will also provide radioactive ion beams of >
100 MeV/u, that will fragment to the most exotic nuclei. The fragmentation
in-flight technique used at FAIR is most interesting for very short-lived nuclei
in the vicinity of the drip-lines and/or for RIB production at very high
energies. FAIR will also provide cooled, stored beams of longer-lived exotic
nuclei.
The
American approach is to combine the features of in-flight and ISOL methods into
one facility: the Rare Isotope Accelerator (RIA). The primary driver of RIA will
be a linac that accelerates protons to 900 MeV and heavy ions to 400 MeV/u. For
ISOL its beam power (of the order of 100 KW) is much smaller than EURISOL (5 MW)
while its maximum heavy-ion energy is much less than FAIR (1.5 GeV/u). A core element of RIA is the use of gas
catcher to stop fragmentation products prior to post-acceleration. This would offer chemistry independent
ISOL beams for long-lived (ms) radionuclides but space-charge effects will limit
the secondary beam intensity.
5.4 A neutrino beta beam facility at CERN
(M. Lindroos)
Figure 39 Beta-beam base line design, partially using
existing CERN accelerator infrastructure (parts in black).
The proposed beta-beam facility [Zucchelli] can be divided into two parts, a low energy part stretching up to 100 MeV/u and a high-energy part for further acceleration and ion stacking and storage in the decay ring, serving as neutrino source. This division is logical as the low-energy part corresponds to the requirements for an ISOL-type radioactive beam factory as proposed and promoted by the European Nuclear Physics community. The high-energy part, serving the neutrino physics community, would be one of several users of such a radioactive ion beam facility and would consequently share the cost and operation of the low-energy part with other physics applications.
The radioactive ions 6He and 18Ne will be produced in an ISOL system using the proposed Superconducting Proton Linac (SPL) as a driver. Following production, the ions will be fully stripped, bunched and accelerated with a linac to approximately 100 MeV/u. Further bunching will be achieved by multi-turn injection into a Rapid Cycling Synchrotron (RCS), followed by acceleration to 300 MeV/u before injection into the Proton Synchrotron (PS). The beam will then be accelerated in several bunches to PS top energy, transferred to the Super Proton Synchrotron (SPS) and accelerated to the desired top energy. Finally, the ions will be transferred to the decay ring where they will be merged with the already circulating bunches through a longitudinal stacking procedure.
Several bottlenecks exist in this process, not least the bunching at low energy, space-charge limitations in PS and SPS, decay losses along the accelerator chain and the longitudinal stacking procedure at high energy in the decay ring.
5.4.1 Ion production
The flux at the detector depends on the average energy of the neutrinos at rest as this determines the focusing of the neutrino beam. A further constraint is set by the decay losses in the accelerator chain that increase with shorter life-time and another aspect to consider are the decay products that could create long lived contamination in the low-energy part. All constraints together point towards two isotopes of particular interest, 6He to generate electron anti-neutrinos and 18Ne for electron neutrinos.
Both species can be produced in large quantities through the so-called ISOL method. The helium isotope is best produced in a BeO target using a very intense primary proton beam of a few GeV, impinging on a so-called neutron converter. For the neon isotope, spallation in a MgO target with a less intense proton beam, hitting the target material directly, is the method of choice. Due to the use of converter technology typically ten times more helium than neon isotopes can be produced.
5.4.2 Ionization, bunching and pre-acceleration
The ions can be transported away from the ISOL target directly in gas form since the chosen elements are noble gases. Alternatively, a high efficiency (for noble gases) mono-charge ECR source, close to the target, can be used to transport the singly charged ions using classical beam transport. In either case the beam has subsequently to be ionized and bunched for further acceleration in the injector chain.
Efficient bunching (<20 ms pulse length) and full stripping of a high-intensity beam can be achieved using a high-frequency 60 GHz ECR source.
Once fully stripped, the ions are first
accelerated in a linac to increase their lifetime. The acceleration of
high-intensity radioactive ion beams to ~100 MeV/u using a linac has
already been studied within the EU-financed study EURISOL. This study is planned
to continue as design study within the 6th EU framework
programme.
5.4.3 Stacking
The energy of the beta-beam neutrinos will be in the range of atmospheric neutrinos. As the time structure of the neutrino beam mirrors the one of the ions circulating in the decay ring, the beam has to be concentrated in as few and as short bunches as possible to permit efficient background suppression in the detector. Four bunches, each 10 ns long, were chosen for the base line design.
A new scheme of longitudinal stacking has been proposed for the beta-beam. It uses asymmetric bunch pair merging, which relies on a dual-harmonic rf system to combine adjacent bunches in longitudinal phase space such that a fresh, dense bunch is embedded in the core of a much larger one with minimal emittance dilution. The fact that only the central part of the residing bunch is affected results in a net increase of the core intensity. The surrounding “older” ions are pushed out, towards the bucket separatrix, where the “oldest” ions will eventually be lost. Asymmetric bunch pair merging has recently been demonstrated in the PS.
5.4.4 Intensity
Starting from the production rates for 6He and 18Ne at the ECR source, and taking into account only beta-decay losses, the beam intensities along the accelerator chain can be calculated. Table 11 quotes the estimated production rates at the source, the beam intensities at extraction from the synchrotrons in the injector chain and the average circulating beam intensities in the decay ring for the beta-beam baseline scenario, assuming 16 Hz operation of the RCS and 8 s cycling time of the SPS and the complete injector chain. The number of batches required to fill the downstream machine is also indicated.
Table 11: Ion intensities for 6He and 18Ne operation along the accelerator chain for the beta-beam base line scenario (only beta-decay losses are taken into account).
|
Machine |
6He ions extracted |
18Ne
ions extracted |
Batches |
|
Source |
~2 ´1013 /s
|
~8 ´ 1011
/s |
dc |
|
RCS |
1.0
´
1012 |
4.1 ´
1010 |
16 |
|
PS |
1.0
´
1013 |
5.2 ´
1011 |
1 |
|
SPS |
9.5 ´
1012 |
4.9 ´ 1011 |
¥ |
|
Decay Ring
|
2.0 ´
1014 |
9.1 ´
1012 |
- |
Experience from operation of high intensity ion beams at CERN suggests that, in addition to the decay losses quoted in Table 11, around 50% of the beam will be lost along the accelerator chain. Applying this rule of thumb shows that in the decay ring typical average ion intensities of 1 ´ 1014 for 6He and 4.5 ´ 1012 for 18Ne can be expected.
5.4.5 Decay losses
The most important difference between the acceleration of stable ions and radioactive ions are the beam losses induced by the radioactive decay during the acceleration process, especially at low energies. The isotopes proposed for the beta-beam have been chosen such that no long-lived activity is left to contaminate the accelerator chain.
A first
study based on simulation of ion losses in the decay ring for the conceptual
design yields that the induced dose rate in the arcs is limited to
2.5 mSv/h after 30 days of operation and 1 day of cooling down
time. It was also shown that the induced radioactivity in ground water will have
no major impact on public safety. The study demonstrated that the decay losses
in the injector chain will be below the commonly accepted power limit of
1 W/m for hands on maintenance, except for the PS. The analysis of losses
in the PS and their consequences clearly deserves more attention. Obviously the
losses in the decay ring are much higher and special care will have to be taken
in the design to cope with this problem.
5.4.6 Planned R&D
The present design is mainly based on available technology with some conservative extrapolations. The studies of the physics reach of such a facility has shown that it is highly desirable to increase the electron neutrino flux by an increase of number of Neon ions in the decay ring. This could feasibly be achieved by the use of several ISOL targets in tandem making use of the same primary driver beam as only a part of the total beam energy is lost in each individual target unit. Furthermore, the accumulation at low energy can clearly be improved for the longer lived Neon ions (originally optimised for He). Another direction for R&D is driven by the recent discovery that a beta-beam facility at higher neutrino energy (corresponding of a decay ring gamma of approximately 500) has an enlarged physics reach comparable to a neutrino factory. The main challenge for such a high gamma facility is the initial acceleration of the ions which today is limited by the maximum magnetic rigidity of the SPS. Beam losses and radiation aspects have clearly been identified as major concerns that will require special attention during the detailed design work.
6
Particle Physics case – neutrino
oscillations
6.1 Overview of neutrino oscillation physics
(A. Blondel, S. Geer, P. Hernandez, A. Rubbia)
In recent years exciting experimental discoveries have shown that neutrino flavors oscillate, and hence that neutrinos have nonzero masses and mixings. The Standard Model needs to be modified to accommodate neutrino mass terms, which require either the existence of right-handed neutrinos to create Dirac mass terms, and/or a violation of lepton number conservation to create Majorana mass terms. The observation that neutrino masses and mass-splittings are tiny compared to the masses of any of the other fundamental fermions suggests radically new physics, which perhaps originates at the GUT or Planck Scale, or perhaps indicates the existence of new spatial dimensions. Whatever the origin of the observed neutrino masses and mixings is, it will certainly require a profound extension to our picture of the physical world. The first step towards understanding this new physics is to pin down the measurable parameters, and address the first round of basic questions:
- Are there only three neutrino flavors, or do light sterile neutrinos exist? Are there any other deviations to three-flavor mixing?
- There is one angle q13 in the mixing matrix, which is unmeasured. Is it non-zero?
- We do not know the mass-ordering of the neutrino mass eigenstates. There are two possibilities, the so-called “normal” or “inverted” hierarchies. Which is right?
- There is one complex phase d in the mixing matrix, which is accessible to neutrino oscillation measurements. If both q13 and sin d are non-zero there will be CP Violation in the lepton sector. Is sin d non-zero ?
- What precisely is the value of the lightest neutrino mass and are neutrino masses generated by Majorana mass terms, Dirac mass terms, or both ?
All of these questions, with the exception of the last one, can in principle be addressed by accelerator-based neutrino oscillation experiments. However, getting all of the answers will not be easy, and will require the right experimental tools. A Neutrino Factory or a Beta-Beam appear to be the ultimate tools for probing neutrino oscillations. Hence the interest in these new types of neutrino sources.
On the experimental side, a new generation
of long baseline oscillation experiments are required that are able to measure
the small oscillation probabilities 
in the
atmospheric range. This will require neutrino beams with unprecedented
intensity, therefore the need of a new megawatt proton source.
The first step in all the various
alternatives that have been proposed would be to use the pions and kaons to
produce a conventional neutrino superbeam (SB). The increase in intensity of the
proton source cannot be fully exploited however with this type of beams, because
systematic errors associated with the irreducible beam background dominate
(there is always a poorly known 
component in the dominant nm
beam. Purer neutrino beams, such as those produced
from muons in a Neutrino Factory (NF) [nufact], or boosted heavy ion
b decays as in the
b-beam (BB) [Zucchelli],[bbcern], could improve things very
significantly. In contrast with a conventional beam, these are essentially pure
beams where the fluxes are known with a very good precision since they are
essentially fixed from the number of muons/Ions decaying in the decay ring and
the well-known kinematics of muon/ion decay.
Figure 40 Left: 
fluxes in the BB from 1018 18Ne and 3
1018 6He ion decays per year at g=100;60 and L=130 km.
Right: 
fluxes at the NF from 2 1020 50GeV m+ , m- decays and L=3000 km.
Figure 40 shows the neutrino fluxes as a function of the energy for a typical NF design and the standard BB design.
On the theoretical side, the lightness of the neutrinos seems to point to a new hierarchy problem in the flavour sector: why are neutrinos so much lighter than the remaining leptons ? There is a hint to understand this from the basic symmetries of the SM. All the fermion masses originate from the interaction with the Higgs field, however while for the fermions carrying colour and electromagnetic charge the coupling has to be of the Yukawa type in such a way that masses are proportional to the vacuum expectation value of the Higgs field (mf = lf v), for neutrinos another type of coupling is possible:
Figure 41 Coupling allowed for neutrinos in the Standard Model, which is not allowed for the other fermions.
This coupling results in Majorana masses for the light neutrinos of
the type mn
= ln
v2 /M , involving necessarily a new
unknown physics scale, M, much larger than the electroweak scale v, thus
resulting in a natural hierarchy between neutrinos and the remaining leptons.
New dynamics should show up at the scale M, which could explain also other
mysteries of the SM. The mass M is interestingly close to the Grand Unified
scale and is associated with the breaking of a global symmetry of the SM, the
total lepton number. This opens new interesting possibilities to explain the
matter-antimatter asymmetry in the Universe.
Unfortunately the scale M is probably too high
to be reached in future accelerator experiments, thus the importance of
extracting all the information available at low energies where the effects of
the scale M are all encoded in the neutrino mass matrices. These matrices
contain a number of new physical parameters: besides the three neutrino masses,
there are three mixing angles, q12, q13, q23,
and CP-violating phases [PMNS]. If neutrinos get masses via Yukawa
couplings, there is only one such phase, d, while in the Majorana case, there are two
more phase observable at low energies. In other words, the lepton flavour sector
of the SM is at least as rich as the quark sector.
Solar and
reactor experiments [Fukuda01],[Apollonio03] have determined the difference
between the squared masses of two of the neutrino mass eigenstates, Dm212
» 8 10-5
eV2 and one of the mixing angles,
q12 »
320 .
Atmospheric neutrino experiments [Fukuda98], and the K2K experiment [Ahn03] on
the other hand have measured the other mass square difference Dm223
» 2.5 10-3
eV2 and the angle q23 , which turns out to be very close to maximal
(450).
In spite of
this impressive experimental progress, we are still far from having the complete
picture. Besides the improvement in precision on the parameters that have
already been measured (which should for instance answer whether the angle
q23 is truly maximal, since this could
point to a new fundamental symmetry), it is necessary to establish the
three-family mixing picture, which requires the measurement of the third mixing
angle q13
presently only bounded to be below
~100 ).
Very important will also be to establish if there are new phases that violate CP in the lepton sector of the SM and to measure the sign of Dm223 that determines the type of neutrino spectrum (hierarchical if the neutrinos 1 and 2, which have the highest ne content, are lighter than the remaining one or inverse hierarchical if they are heavier. Fortunately all these questions can be addressed in more precise long baseline neutrino oscillation experiments. Other fundamental questions like the determination of the absolute neutrino mass scale and the Majorana nature of light neutrinos requires a new generation of experiments measuring the end-point of Tritium b-decay and searching for rare neutrinoless double b-decay.
6.1.1 Neutrino Factory Physics Program
The
possibility of having intense neutrino beams of well-known composition opens the
road to a large variety of physics studies. Having a simultaneous beam of
electron and muon neutrinos, distinguished by helicity, allows the study of
several oscillation processes. If
we consider negative muons in the ring, the following transitions can
occur:
disappearance
appearance
appearance
disappearance
appearance
appearance
An
important feature of the Neutrino Factory is the possibility of having opposite
muon charges circulating in the ring, therefore allowing also the study of the
charged-conjugated processes of those above.
Since measurements can be made with both positive muons or negative muons stored, 12 measured differential spectra can be simultaneously fit to the oscillation parameters. This would provide experiments with a wealth of measurements that, in addition to offering exquisite precision, also offer the flexibility to exploit possible surprises.
The simultaneous presence of both neutrino flavours in the beam poses the problem of separating neutrinos due to oscillations from beam background. A simple identification of the lepton produced in charged-current interactions is not sufficient, since muons, for instance, could come from the antineutrino component of the beam, or from the oscillation ne®nm , or even from the oscillation ne ®nt followed by the decay t®m. The obvious way to distinguish neutrinos coming from the beam from those coming from oscillations is to measure the charge of the lepton produced in charged-current events. This can be done readily using a magnetic detector of design similar to that of the CDHS or MINOS experiments, for which by that time one can safely assume that it could be built with a mass of the order of 50 ktons. Many studies have been performed under this hypothesis, where the main discovery channel is the ‘wrong sign muon’ also called golden channel [Cervera00].
The ideal case would be to be able to
measure the charge for both electrons and muons, and perhaps find a way also to
identify taus. Since the last two requirements are quite difficult to match, we
consider as a default case that the detector for the neutrino factory will only
be able to identify the charge of muons.
If also electron identification can be performed, as would be the case in
a large liguid argon detector ([Bueno00], see also chapter
6.4) , the detected events can be classified in four
classes:
Charged-current electrons,
Right-sign muons,
Wrong-sign muons,
Events with no leptons.
An example
of the set of energy spectra for these classes, for positive and negative muons
circulating in the ring, is given in Figure 42.
Neutrino factories are also attractive
because, when compared with conventional neutrino beams, they yield higher
signal rates with lower background fractions and lower systematic uncertainties.
These characteristics enable neutrino factory experiments to be sensitive to
values of q13 that are beyond the reach of any
other approach. Studies (see e.g. [Huber03]) have shown that a non-zero value of
sin2
2q13 could be
measured for values as small as O(10-4). In addition, both the
neutrino mass hierarchy and CP violation in the lepton sector could be measured
over this entire range. Even if q13 = 0 the probability for ne « nm oscillations
in a long-baseline experiment is finite, and a Neutrino Factory would still make
the first observation of ne « nm transitions in
an appearance experiment, and put a sufficiently stringent limit on the
magnitude of q13 to suggest perhaps the presence of a
new conservation law. For the measurement of the quantities q13 and d, it has been shown that
the golden observables are the
oscillation probabilities 
and 
at baselines, L, and energies, En, in the atmospheric
range En /L » Dm223 while
sign(Dm223) can also be determined with the same transitions but require
sufficiently long baselines and high energies so that Earth matter effects
modify the vacuum oscillation probabilities significantly (see Figure 43).
Figure 42
:
Four classes of events studied in a liquid argon TPC with muon charge identification. From the top, left to right: events with high-energy electrons,
right-sign muons, wrong-sign muons,
no charged leptons [Bueno00].
Figure 43 The sensitivity reaches as functions of sin22 q13 for sin22 q13 itself, the neutrino mass hierarchy, and maximal CP Violation (dCP = p/2) for each of the indicated baseline combinations. The bars show the ranges in sin22 q13 where sensitivity to the corresponding quantity can be achieved at the 3s CL. The dark (red) bars show the variation in the result as Dm221 is varied within its present uncertainty. Figure from [Huber03].
6.1.2 Physics Program with beta-beams
The physics program of a low energy beta-beam
was recently discussed in [Bouchez03].
An ECR source coupled to an EURISOL target
would produce 2×1013 6He ions per second. Taking into
account all decay losses along the accelerator complex, and estimating an
overall transfer efficiency of 50%, one estimates that an antineutrino flux
aimed at the Fréjus underground laboratory of 2.1×1018 per standard year
(107 s) is
possible.
For 18Ne, the yield is expected to be only
8×1011 ions per second. Due to this
smaller yield, which could be certainly improved with some R&D, it was then
proposed to use 3 EURISOL targets in sequence connected to the same ECR source.
Again taking into account decay losses plus a 50% efficiency, this means that a
neutrino flux of 0.35×1018 per standard year is
achievable.
All these numbers are preliminary and need to
be refined. They are however based
on the present state of the art for the technology, and suppose using the
present PS, while the SPS cycle is set at 16 s; a shorter cycle for the SPS
would improve the accumulation factor substantially, while a faster PS would
increase the intensity of ions making it to the decay
ring.
For the present study, it was supposed that the
neutrino flux from 18Ne
could be increased by a factor 3 over the
present conservative estimate, having room for improvements both in the cycle
duration of PS and SPS and in the 18Ne
production at the
targets with a dedicated R&D, while only a 40 % improvement was put on
antineutrino fluxes. One assumed
that that a UNO-like water Cerenkov detector (440 kt fiducial mass) will be
installed in the underground Fréjus laboratory and receive neutrino beams
produced at CERN, 130 km away.
The
neutrino beam energy depends on the g of the parent ions in the decay ring. The optimization of this energy, is a
compromise between the advantages of the higher g, as a better focusing, higher cross sections
and higher signal efficiency; and the advantages of the lower g values as the reduced background
rates (see the following) and the better match with the probability
functions. Given the decay ring
constraint: g(6He)/g(18Ne)=3/5 the optimal g values result to be g(6He
)=60 and g(18Ne
)=100. A flux of
2.9×1018 6He
decays/year and 1.1×1018 18Ne
decays/year, will be assumed. Figure 44 shows the BetaBeam neutrino fluxes computed at the
130 Km baseline, together with the SPL Super Beam
(SPL-SB).
The mean neutrino energies of the ne, ne beams are 0.24 GeV and 0.36 GeV
respectively. They are well matched with the CERN-Frejus 130 km baseline. On the
other hand energy resolution is very poor at these energies, given the influence
of Fermi motion and other nuclear effects and in the following all the
sensitivities are computed for a counting experiment with no energy cuts.
Figure 44 : Beta Beam fluxes at the Frejus location
(130 km baseline). Also the SPL Super Beam nm and nm fluxes are shown in the plot
[Bouchez03].
The signal in a Beta Beam looking for
ne®nm
oscillations would be
the appearance of nm charged-current events, mainly via
quasi-elastic interactions. These
events are selected by requiring a single-ring event, the track identified as a
muon using the standard Super-Kamiokande identification algorithms (tightening
the cut on the pid likelihood value), and the detection of the muon decay into
an electron. Background rates and signal efficiency have been studied in a full
simulation, using the NUANCE code, reconstructing events in a
Super-Kamiokande-like detector.
The Beta Beam is intrinsically free from
contamination by any different flavor of neutrino. However, background can be generated by
inefficiencies in particle identification, such as mis-identification of pions
produced in neutral current single-pion resonant interactions, electrons
(positrons) mis-identified as muons, or by external sources such as atmospheric
neutrino interactions.
The pion background has a threshold at neutrino
energies of about 450 MeV, and is highly suppressed at the Beta Beam
energies. The electron background
is almost completely suppressed by the request of the detection of a delayed
Michel electron following the muon track. The atmospheric neutrino background
can be reduced mainly by timing the parent ion bunches. For a decay ring
straight sections of 2.5 km and a bunch length of 10 ns, which seems
feasible, this background becomes negligible. Moreover, out-of-spill neutrino
interactions can be used to normalize this background to the 1% accuracy
level.
Signal and background rates for a
4400 kt-yr exposure to 6He and 18Ne beams, together with the SPL
SuperBeam (SPL-SB) fluxes, are reported in Table 12.
Table 12 :
Event rates for a 4400 kt-y exposure. The signals are computed for
q13
=3°, d=90° sign(Dm2)=+1. “d-oscillated” events indicates the difference
between the oscillated events computed with d=90° and with d=0. “Oscillated at the Chooz limit” events are
computed for sin22q13=0.12, d=0.
|
|
Beta
Beam |
|
SPL-SB |
|
|
|
6He(g=60) |
18Ne(g=100) |
nm(2 yrs) |
nm(8 yrs) |
|
CC events (no
osc, no cut) |
19710 |
144784 |
36698 |
23320 |
|
Oscillated at
the Chooz limit |
612 |
5130 |
1279 |
774 |
|
Total
oscillated (d=90°, q13
=3°) |
44 |
529 |
93 |
82 |
|
d
oscillated |
-9 |
57 |
-20 |
12 |
|
Beam
background |
0 |
0 |
140 |
101 |
|
Detector
backgrounds |
1 |
397 |
37 |
50 |
A facility
where the neutrino fluxes are known with great precision is the ideal place
where to measure neutrino cross sections. In the Beta Beam the neutrino fluxes
are completely defined by the parent ions beta decay properties and by the
number of ions in the decay ring. A close detector of ~1 kton placed at a distance of about
1 km from the decay ring could then measure the relevant neutrino cross
sections. Furthermore the
g factor of the accelerated ions can be varied.
In particular a scan can be initiated below the background production threshold,
allowing a precise measurement of the cross sections for resonant processes. It
is estimated that a residual systematic error of 2% will be the final precision
with which both the signal and the backgrounds can be evaluated.
The q13
and d sensitivities are computed taking
into account a 10% error on the solar dm2 and sin22q, already reached after the recent SNO-salt
results and a 5% and 1% error on dm223 and sin22q23 respectively, as expected from the
J-Parc neutrino experiment. Only the diagonal contributions of these errors are
considered. In the following the default values for the oscillation parameters
will be sin22q23=1, dm223
=2.5×10-3eV2, sin22q12=0.8, dm212
=7.1×10-5eV2, sign(Dm2)=+1.
The q13
angle can be
independently explored both with neand ne disappearance measurements. We note
that the comparison of the neand nedisappearance experiments could set
limits to CPT violation effects. Sensitivities to q13
, computed for a 5 yr
run and for systematic errors equal to 2%, 1% and 0.5% are shown Figure 45left). For comparison sake, shown in the same plot are
the sensitivities reachable with the appearance channels, computed for
d=0.
Indeed q13
and d are so tightly coupled in the
appearance channels that the sensitivity expressed for d=0 is purely indicative. A better understanding of the
sensitivity of the BetaBeam is expressed in the (q13
,d) plane, having fixed all the other
parameters (dm223
=2.5×10-3 eV2), as shown in Figure 45 right). In the same plot the sensitivity of the
SPL-SB computed for a 5 yrs nmrun is displayed. It can be noted
the very large variation of the SPL-SB sensitivity for the different values of
d, characteristic of the single flavour
run. The BetaBeam, having both CP
neutrino states in the same run, exhibits a much more favourable dependence to
the CP phase d.
Figure 45 :
Left: 90%CL sensitivity of
the disappearance channel to q13
in a 5 yrs run drawn as dotted lines. The labels 0.5%, 1% and 2% indicate the
systematic errors with which are computed.
Also shown are the appearance sensitivities of Beta and SPL beams,
computed for d=0, sign(Dm2)=+1. Right: 90%CL sensitivity expressed as function
of d for dm223
=2.5×10-3eV2. All the appearance sensitivities are computed
for sign(Dm2)=+1.
A search for leptonic CP violation can be
performed running the Beta Beam with 18Ne and 6He, and fitting the number of
muon-like events to the p(ne®nm)
and to the
p(ne ®nm
) probabilities. Event
rates are summarized in Table 12. The region of 99% CL sensitivity to maximal CP
violation (d=90°) in the dm212
and q13
parameter space is
plotted in Figure 46.
Figure 46 : 99%CL d sensitivity of the Beta Beam, of the
SPL-SuperBeam, and of their combination, see text. Dotted line is the combined SPL+Beta
sensitivity computed for sign(Dm2)=-1. Sensitivities are compared with a 50 GeV
Neutrino Factory producing 2×1020m decays/straight section/year, and two 40 kton
detectors at 3000 and 7000 km
6.1.3 Potential improvements in the physics program optimization
Performing measurements at potential neutrino factories or beta-beams
will certainly face several difficulties. On the theoretical side, the existence
of correlations and degeneracies in parameter space
[Cervera00],[Burguet01],[Minakata01],[Barger02] make the simultaneous
determination of all the unknowns rather difficult. The importance of having
good neutrino energy resolution or combining the measurements of the golden oscillation probabilities at
several experiments with different < En /L > (or
different matter effects) have been proposed to overcome this problem
[Burguet01],[Barger02], [Burguet02]. Alternatively the measurement of the silver channels [Donini02] 
besides the golden
one, although it is experimentally more challenging, is extremely powerful in
reducing these correlations. The silver channel also provides a test of
unitarity of the Neutrino mixing matrix!
In fact, it has been shown that while the combination of BetaBeam and
SuperBeam could not help in solving the degeneracies, the combination of one of
them with the Neutrino Factory Golden and Silver channel can, instead, be used
to solve completely the eightfold degeneracy.
Figure 47
Solving degeneracies (from [Rigolin04]). The parameter space shown is the
variation {Dq13, dCP} around the true solution in
the {q13, dCP} plane. The lines show the locus
where the same number of events would be observed. Full lines, neutrino
exposure; dashed lines antineutrino exposure. On the left, the red and blue
lines show two different base lines (730 and 3500 km) while on the right the red
and blue lines show the golden and silver channel.
Typically both in the NF and BB designs, the energy of the parent muon/ion (which is proportional to the average neutrino energy) can be optimized within a rather large range, since this is fixed by the acceleration scheme that is part of the machine design. Once the energy is fixed, the baseline is also fixed by the atmospheric oscillation length. This optimization is however a complex problem because there are often contradicting requirements in the maximization of the intensity, the minimization of backgrounds, having useful spectral information, measuring the silver channel besides the golden one, having sizeable matter effects, etc.
This optimisation was done for the NF some years ago and a muon energy of Em =20-50 GeV and a baseline for the golden measurement of a few thousand kilometres is considered a reference setup [Cervera00]. The combination of this measurement, using a 40 KTon iron calorimeter [Cervera00a], plus the silver one in an Opera-like tau-neutrino detector [Donini02] results in a great physics potential. The sensitivity to sin2 q13 is below 10-4 and there is a 99% CL discovery potential for CP violation if d> 100. In addition, the atmospheric parameters can be determined with a 1% precision and the sign of Dm223 can be measured in a large range of parameter space.
In contrast the standard CERN-based b-beam design as conceived by P. Zucchelli [Zucchelli] was intended to use much of the CERN infrastructure. In particular the ions, once produced at a new Eurisol-like facility, would be accelerated at the existing SPS up to a g ~ 150. An appropriate baseline for this energy was identified in the Fréjus tunnel, 130km from CERN, that is by happenstance also an appropriate baseline for the SPL-based superbeam [splcern]. A megaton water Cherenkov could be located in Frejus to serve both purposes. The sensitivity to the parameters q 13 and d in the BB and BB + superbeam setups would improve considerably that of other superbeams under construction [Mezzetto03],[Bouchez03], such as T2K at JPARC [Itow01] or NUMI [NUMI], as shown in Figure 45, but it is still limited compared to the ultimate sensitivity in the NF, in spite of the fact that the difference in fluxes between the NF and BB of Figure 40 should be essentially compensated by the bigger detector mass considered in the superbeam-BB case.
It has been recently realized that provided a more ambitious acceleration scheme for the ions were possible, there is an enormous gain in the physics potential of the b-beam if the energy could be increased by a factor 5-10 and the baseline accordingly [Burguet03]. As in the NF, the higher energy results in a higher intensity, because of the larger neutrino cross sections, in a better measurement of the neutrino energy, which reduces parameter correlations and degeneracies and finally the longer baseline makes the measurement of the sign of Dm223 possible.
Higher energy b-beam at CERN would imply
accelerating the ions in the LHC or an upgraded SPS, and the corresponding high
energy storage rings. Given their promising physics performance, the feasibility
of these options needs to be further studied.
6.2 A possible large underground laboratory: status and plans of the Fréjus international laboratory
(L. Mosca, A. Rubbia)
An intense activity of tunnel excavation will take place in the Fréjus area during the next few years and in particular a safety tunnel parallel to the Fréjus road tunnel, at the French-Italian boarder, was approved in December 2001 and its excavation should start at the beginning of the next year (2005). The diameter of this tunnel, with a present nominal value of about 5.5 m, is currently in the final stage of negotiation between the French and Italian Transport authorities. A series of 34 bypasses will connect the safety tunnel to the road tunnel. The end of the construction of the safety tunnel (without the bypasses) is planned around 2008-2009. This situation creates the opportunity to build a very large cavern near the existing laboratory LSM (“Laboratoire Souterrain de Modane”) half way, 6.5 km from both the French and the Italian entry of the tunnel. A laboratory at this location has the advantage of double horizontal access, clearly symmetrical bi-national and European symbolism, large depth (4800 mwe), good quality of the rock (hardness and absence of water problems) and strong support from the local authorities (Regions Rhône-Alpes and Piemonte) and the Fréjus Tunnel Companies. Its major current difficulty is the perception of a possible conflict with the functionality of the safety tunnel on the French Transport Authority side. In the case this is confirmed the transport authorities recommend the excavation of a third separate tunnel to reach the area of the construction of the cavity (and evacuate the rock of the excavation), while the access after the construction could be done through the safety tunnel. This extra tunnel would of course increase the cost of the installation (cavity plus detector) by 10 to 20%. It is also interesting to note that the beam associated and moving to a shallower region and therefore reducing the extra excavation costs do not seriously affect proton decay physics potential. There is, for instance, at 3km from the French entrance an overburden of 2500 mwe. In conclusion this is the preferred site and studies of feasibility and functional compatibilities are in progress.
A more prospective scenario considers the opportunity created by the Lyon-Turin TGV 52 Km long tunnel crossing the Fréjus region. While the tunnels (one for each direction) are planned to enter in an operational phase in 2015-2020, a few reconnaissance galleries have been approved and funded. In particular the Venaus gallery (5.5 m diameter), starting in the SUSA area (Italy) is a 7 km long gallery (possibly extended to 10 km). The end of this gallery is situated near the French/Italian boarder. It will be excavated between the two train tunnels and the end of its construction is expected in 2008. The gallery has a large overburden going from 4800 mwe at around 7 km from the entrance to 7000 mwe at the end of 10 km, making it eventually the deepest laboratory in the world. In this scenario while there is no serious compatibility problems with the train operation and safety according to the tunnel engineers[1], one has a single-sided access, posing safety concerns for the laboratory users and also breaking the bi-national symmetry. This option is disfavoured by the INFN for the reasons stated above and also due to possible conflicts with other national scientific policy options.
6.3 A megaton water Cherenkov detector
(C. K. Jung, K.
Nakamura, V. Palladino)
A well organized
international effort, joining the forces behind the Hyper-K [Hyper-K] project in Japan,
the UNO project in USA and the Frejus project in Europe [Mosca], with common
physics goals and strong mutual support of each local initiative, can seriously
hope to bring a successful experiment somewhere in the world and carry out a
far-reaching, comprehensive neutrino physics and nucleon decay
program.
Figure 48 UNO Detector Conceptual Design
A
Megaton Water device can rely on a reasonable extrapolation of a proven
technology and could be built within a predictable R&D and then construction
time. Water is the cheapest detector material. The international community is
persuaded that an affordable design, not higher than 500 M$ or so, will be
possible and is determined to embark coherently first in a final common R&D
phase and then in the construction of such a large detector somewhere in the
world, where the realisation of a home underground laboratory, capable to host
and operate it, will indeed prove possible. It could do physics 10 years after
approval.
The basic design of UNO is
(Figure 48) a triplet of
adjacent, only optically separated, 60x60x60
m3 water
tanks, 650 kton in
total, (440 kton fiducial, 20 times SuperK) equipped with 56000 20” PMTs and
14,900 8” PMTs, with surface coverage 40% (as SuperK) in the central tank and
10% in the two wing tanks. The design, optimized to comply with 1) light
attenuation length limit 2) PMT water pressure limit 3) cost constraints and built-in
staging, involved 98
physicists, from 40 Institutions, in 7 countries. The Hyper-Kamiokande design is
very similar (Figure
49). It could be called DUE, as it consists essentially
of two independent similar detector units, in two twin cylindrical galleries,
each 48m ×
50m
×250m, reaching a 1
Mton total mass equipped with 100000 PMTs each.
Figure 49 Conceptual Design of Hyper Kamiokande
Multiple smaller
detectors appear less convenient. They would 1) be more expensive, the larger
surface to volume ratio would require more PMTs 2) provide less total fiducial
volume 3) imply more drifts and auxiliary/service space, specially expensive to
excavate and finish 4) have smaller energy containment
In addition, for
same pmt coverage, the larger detector has a finer effective granularity and
therefore better pattern recognition, particle identification, position and
angular resolution.
The main challenges
to tackle for a Megaton detector appear at the moment
1)
to secure an
adequate and realistic site
It should be
conveniently located with respect to MMW accelerators. It has to bring no
environmental concern. It has to have a vast infrastructure of modern underground technologies The excavation
we need has to be half the detector cost, or so. It should be 4000mwe deep or
more, to be useful for solar and supernova neutrino
studies.
2)
to keep the general
cost affordable. Cost containment is the key issue.
About half of the
cost is the big PMTs, pricd still 2.7 K$ each. 200 K$ or so in total, fully
equipped. Their 8 years delivery time dominates construction time. The next
coming phase of rigorous professional detector design will have to explore all
possible roads to cost reduction. In some areas, photosensors in particular,
this implies a serious R&D effort.
Support for the
R&D towards UNO, identified as an essential HEP facility, has been
repeatedly stated .by major US review panels, from the original statement of the
HEPAP sub-panel in 2001 [HEPAP01] to the recent recommendation of the Intragency
Working Group in April 2004 [Intra04]. NSF is structuring the selection process
of a site for the much recommended multipurpose NUSEL (National Underground
Science & Engineering Laboratory). It should take off within 2004 and fund
the necessary studies.
6.3.1 Detection of neutrinos
A large UNO type detector, 20 to 40 times bigger than Super-K, appears as an inescapable and natural response to the recent “neutrino revolution”, the unequivocal evidence of the existence of neutrino transitions accumulated since 1998.
The Water Cerenkov technique provided the largest share of this evidence [Fukuda98] [K2K] and will, no doubt, still be a main player in the future, at least for detection of low energy below 1 GeV or so.
A
new Megaton detector promises a major boost of our observations of atmospheric,
solar, Supernova (burst and relic) and astrophysical neutrino phenomenona. In
conjunction with new superior sources of low energy neutrinos, Superbeams and
Betabeams, it also promises oa similar boost of our experimental knowledge of
neutrino mass splitting, mixings and CPV phase. This phase may be the first
experimental signal of the type of mechanisms that may have induced primordial
leptogenesis and later
matter-antimatter asymmetry.
With a Megaton
neutrino observatory, detection reach of
SuperNova (SN) will extend to the local group of galaxies, to about 1 Mpc. A
galactic SN explosion should provide, once every 30 years, a detectable burst of
up to 140K neutrino events, with its msec timing
structure of the flux, resulting in precise
observation of explosion process and neutrino mass test
<~1eV
SN relic could be
detected (or all models ruled out) in about 4 years of UNO running at 4000 mwe.
Moving to
atmospheric neutrinos, the superior containment of a Megaton device would permit
spectacular evidence for a disappearance minimum in L/E of high energy
atmospheric muon neutrinos, measuring Dm23 to
far better than 1%, from 7 years of
UNO (enriching the sample of higher energy muons that permit a precise
determination of the neutrino path L)
Most relevantly to
the Workshop, however, the detector matches beautifully
the characteristics of MMW power neutrino conventional (super)beams as well as
novel betabeams. For such neutrino events of 1 GeV or lower, producing little or no pions, one has good efficiency and separated identification
of muons , electrons (and photons). This is
essential for the study of the subdominant oscillation channel
nm « ne, , that holds all the remaining secrets of the
leptonic mixing and CPV pattern. The megaton mass compensates for the reduced
fluxes possible with low energy neutrino beams. Many specific
studies have been performed for several combinations of neutrino beam power and
baselines (4MW JPARC superbeam to the HyperK site at 300 Km [T2K], 4MW CERN-SPL superbeam and betabeam to
the Frejus site at 135 Km [ECFAreport], 1 MW BNL-AGS to a Western US site at
2000-4000 Km[BNLnu]). We really ought to make at least one of them reality.
The location of a
Western site in the US has generated a significant amount of studies and surveys
(Figure 50). The most promising site, offering the largest asset
of existing experience and infrastructures (among them the high speed, large and
long, conveying shafts system essential for effective evacuation of the
excavated rock), appears at the moment the Henderson site, a modern, environment
conscious, molybdenum mine in Colorado. This offers a shelter of 5000 mwe,
excellent connections and a lively atmosphere, not far from Denver. If favorable
geological conditions are confirmed, UNO would require a 116 M$ dedicated large
volume excavation.
Figure 50 Candidate sites for the US National Underground Science &
Engineering Laboratory (NUSEL)
6.3.2 Proton decay
A large UNO type detector
has, however, an independent and equally compelling motivation: it appears also
as the next natural step to superior sensitivity to nucleon decay and thus to a
new mass scale in the GUT region. The minuscule mass splittings measured, by
means of the neutrino oscillation wavelength, also favour a new mass scale of
GUT nature. This unique scientific and technical synergy between neutrino
oscillations and nucleon decay,
astro-, nuclear and
particle physics, accelerator and non-accelerator physics has been, since 1999,
the theme of the NNN (Next Nucleon decay & Neutrino detector) series of
Workshops [NNN]. Figure 51
gives a snapshot of
the past, present and possible future, both experimental and theoretical, of our
understanding of nucleon decay.
Figure 51 Our past, present
and possible future knowledge of nucleon decay.
Candidate events
for proton decay to ep0
must cluster around
zero total reconstructed
vector momentum p
and total
reconstructed invariant
mass M around 940 MeV/c2. Smearing will result from, bound nucleon
effects, Fermi momentum and binding energy corrections,. The SuperK sensitivity
to partial decay lifetime t/B (5.7 1033
years at 90%CL, for the present 79 Mton-years total exposure) is
ultimately limited by an (atmospheric) background rate of fake decay candidates
of 2.2 events/Mton year, based on K2K beam data. This is due to the looseness of
the 2D cuts, in p and M, affordable while keeping sizeable (43%) detection
efficiency. UNO or HyperK will be able to afford much tighter cuts: with still
17% efficiency, selecting essentially only free nucleon decays, the limiting
background will reduce to 0.15 fake events/Mton year. With a total UNO exposure
larger than 8 years, the sensitivity of a new much larger detector will extend,
by more one order of magnitude, to a partial lifetime above 1035
years.
The best
sensitivity to proton decay to Kn is obtained with
the coincidence method (among the prompt photon emitted when an 16O
proton decays and the delayed m and then electron
signals from K decay to
mn). This is then
slightly enhanced by the K to p
p0
method and the
m spectrum in method
in mn decay . The
limiting background is atmospheric n production of
KL pairs, about 1
event/Mton-year. 10 years of UNO would set a partial lifetime limit larger than
1034 years (1.6
10.33 presently).
6.3.3 R&D areas. Photosensors.
Detailed geological
survey, drillings for final rock characterization, environmental assessment,
long term liability issues have to be performed for all serious candidate
sites
Solutions for rock
surface treatment/water containment are to be understood. Simple geo membrane
liners are being weighed against
more durable treatment with steel frames and concrete coating with
membrane seal.
PMT mounting
schemes are being studied, taking into account the pressure limits,
unfortunately well know now. PMT cost reduction schemes are to be studied for
conventional PMTs, in collaboration
with Hamamatsu and possibly other producers. Simpler structures like spherical
PMTs are being seriously considered. While PMTs remain the baseline realistic
device, alternative photo-sensors are to be investigated too.
In a talk
immediately before the Workshop, K. Nakamura described the HyperK program for
development of large Hybrid Photo Detectors (HPD) in collaboration with the
Hamamatsu Electron Tube Center. It
aims at
developing high sensitivity at low cost per unit sensitive area. The initial
idea of developing a 40 “ PMT was abandoned after the SuperK accident and
focused on simpler structures like HPDs, that may be cheaper anyway. These
replace the traditional chain of dynodes with electron bombardment in silicon,
producing e-hole pairs, followed by avalanche multiplication. Noise,
traditionally due mostly to the
first dynode, is strongly reduced and sensitivity to single photon can be
reached. Currently
available HPD from Hamamatsu
are very small. A 5” prototype was produced and fully characterized:
quantum efficiencies and time response data exist. A 13”
prototype is now ready (Figure 52). Development of preamp,
digital filter and analog memory cards also in progress. Finally, ideas for a
20” spherical HPD are rather advanced, but do need much further study.
Figure 52 Recent HPD Prototypes from Hamamatsu
Supported by a DOE
grant, a Reference Photo-sensor (Figure 53) is being studied at UC Davis, in collaboration with
night vision projects. It aims at devices combining optimal light concentration
on the photo-cathode with an optimal photo electron collection lens. Large light
sensitive surfaces could be covered, honeycomb arrangement of many individual
hexagonal devices is suggested.
Figure 53 Reference Photosensor R&D in the USA
Further enhancement
of performance is being sought could by development of better reconstruction
software for Cherenkov rings, based on many years of experience now. More sophisticated
electronics, with wave-form
digitizers and narrower PMT integration time (to reduce scattered light) is
certainly an handle to be exploited.
6.3.4 Conclusions
Based on a proven technology, an underground megaton water Cerenkov detector has a major potential for important discoveries. It would match very well the characteristics of MMW power neutrino conventional beams as well as betabeams A world wide scientific community, made of collaborating regional collaborations, is looking for one (or more) home sites where to build it and exploit it about 10 years after approval. Collaboration is already being explored on all the non site-specific aspects of the necessary R&D
6.4 Ideas for a next generation liquid Argon TPC detector for neutrino physics and nucleon decay searches
(A. Ereditato, A. Rubbia)
In the late 60’s the potentials of liquid noble gases as detection media to realize position sensitive detectors with high spatial resolution was recognized [Doke93] as well as the possibility of using such media for large and performing calorimeters for particle physics experiments [Willis94]. Among the many ideas developed, the Liquid Argon Time Projection Chamber (LAr TPC), conceived and proposed at CERN by C. Rubbia in 1977 [Rubbia77], certainly represented one of the most challenging and appealing designs. The technology was proposed as a tool for uniform and high accuracy imaging of massive detector volumes.
The
feasibility of this technology has been further demonstrated by the extensive
ICARUS R&D program, which included studies about proof of principle, LAr
purification methods, readout schemes and electronics, as well as studies with
several prototypes of increasing mass on purification technology, collection of
physics events (also neutrino events), pattern recognition, long duration tests
and readout. The realization of the 600 ton ICARUS T600 detector culminated with
its full test carried out at surface during the summer 2001 demonstrating that
the technique can be operated at the kton scale with a drift length of 1.5 m
[Amoruso04, Amoruso04b, Antonello04, Amoruso04b, Arneodo03]. The success of the
fully industrial construction of the T600 module and its excellent performance
has justified the idea of cloning the detector to reach the 3000 ton mass scale
(ICARUS T3000). The T3000 detector represents the largest, practical achievable
size by employing a modular approach. On the other hand, modularity was not
imposed by the LAr TPC technique but by the boundary conditions of the LNGS
laboratory.
Having at
disposal the mature technique developed in the context of the ICARUS program,
physics is calling today for at least two applications at two different mass
scales [Ereditato]. On the one hand, ultimate nucleon decay searches and high
statistics astrophysical and accelerator neutrino experiments will require very
large detector masses, of the order of 100 kton. On the other hand, future
precision studies of neutrino interactions, calorimetry and near stations for
long baseline beam experiments will need detectors with masses in the range
of 100 ton. There is a high degree
of interplay and a strong synergy between small and large mass scale
apparatuses, the very large detector needing the small one in order to best
exploit the measurements with high statistical precision that will be possible
with a large mass. Small and very large LAr detectors could certainly play
significant roles in a potential future high-intensity neutrino beam facility.
In particular, the conceptual design of a 100 kton LAr TPC detector is in
progress together with the identification of an R&D
strategy.
The
physics potential of the large LAr detector combined with a neutrino Super-Beam
has been studied. This application profits from the very good granularity
provided by the technique. The optimization of the proton energy and of the
baseline will follow from the overall design and upgrades of the future
accelerator complex hosting the beam and might be accomplished in stages
according to physics advances and/or to the availability of financial resources.
The various neutrino beam optimizations will most likely be performed in
accordance with the global physics program, which could possibly include
nuclear, muon, kaon and neutron physics. However, a 100 kton LAr detector would
provide a general purpose detector able to exploit all kinds of neutrino
Super-Beams.
The
imaging of the events and the high energy resolution in the LAr TPC make the
studies with Beta-Beams very attractive. The possibility to have separately pure
electron-neutrinos and antineutrinos, combined with a massive 100 kton detector
would be an ideal configuration to study neutrino oscillation parameters, in
particular the CP-phase. Optimization studies indicate that the longest possible
baseline is required, as long as matter effects are small, in order to benefit
from the rise of the (anti)neutrino cross-section and the reduction of momentum
smearing introduced by the Fermi motion. The detector must provide good
pion/muon discrimination in order to suppress the NC background with a charged
leading pion. The combination of imaging (tracking and energy) with the
detection of Cerenkov light could provide adequate muon/pion separation.
The
physics potential of a magnetized large LAr detector coupled to a Neutrino
Factory is also very large. The ideal detector should be capable of identifying
and measuring all three charged lepton flavors produced in CC interactions and
of measuring their charges to discriminate the incoming neutrino helicity.
Embedding the volume of Argon inside a magnetic field would not alter the
imaging properties of the detector.
Finally,
one should emphasize that the astrophysical neutrino physics program is
naturally very rich for a 100 kton LAr observatory [Rubbia04]. One expects 10000
atmospheric neutrino events per year and about 100 tau-neutrino CC events per
year from muon-neutrino oscillations. These events are characterized by the
excellent imaging capabilities intrinsic to the LAr TPC and will provide an
unbiased sample of atmospheric neutrinos with an unprecedented quality and
resolution, compared to existing or planned studies based on Cerenkov ring
detection. Solar neutrinos provide about 324000 events per year with electron
recoil energy above 5 MeV. A galactic SN-II explosion at 10 kpc yields about
20000 events. Sensitivity to extragalactic supernovae should be possible as well
as to relic SN neutrinos. A characteristic feature of the LAr TPC is the
accessibility to several independent detection channels which have different
sensitivities to electron-neutrino, electron-antineutrino and other neutrino
flavors. The study of all neutrino flavors from supernova explosion would be
performed in great detail by a LAr detector, in an appreciably better way when
compared to water Cerenkov detectors, which are mainly focusing on the
electron-antineutrino
flavor. Last but not
least, the physics of the nucleon decay. Direct evidence for baryon number
violation represents one of the outstanding goals of particle physics. Nucleon
decay searches require very good knowledge of the backgrounds induced by
atmospheric neutrinos. A target of 100 kton = 6 × 1034 nucleons yields a sensitivity for protons of
tp/Br > 1034 years × T(yr)× e at the 90% CL in the absence of
background. Although the envisioned
detector has a mass of 100 kton, its physics program effectively competes with a
1 Megaton water Cerenkov owing to better event reconstruction capabilities
provided by the LAr technique.
The
possibility to construct and operate a very large LAr TPC is a very complex
technical task. However, it can be shown that a 100 kton detector might be
technically feasible, economically affordable and able to be safely operated. A
single LAr volume is the most attractive solution from the point of view of
construction, operation and cryogenics and is to be favored over the modular
approach. The basic design features of the detector can be summarized as
follows:
1. Single
100 kton boiling cryogenic tanker at atmospheric pressure for a stable and safe
equilibrium condition (temperature is constant while Argon is boiling). The
evaporation rate is small and is compensated by corresponding refilling of the
evaporated Argon volume.
2. Charge
imaging, scintillation and Cerenkov light readout for a complete (redundant)
event reconstruction. This represents a clear advantage over large mass,
alternative detectors operating with only one of these readout modes.
3. Charge
amplification to allow for very long drift paths. The detector is running in
bi-phase mode. In order to allow for drift lengths as long as 20 m, which
provides an economical way to increase the volume of the detector with a
constant number of channels, charge attenuation will occur along the drift due
to attachment to the remnant impurities present in the LAr. One can compensate
this effect with charge amplification near the anodes located in the gas
phase.
4.
Absence of magnetic field, although this possibility might be considered at a
later stage. R&D studies for charge imaging in a magnetic field are on-going
and results are expected soon. Physics studies indicate that a magnetic field is
really only necessary when the detector is coupled to a Neutrino Factory.
The
cryogenic features of the proposed design are based on the industrial know-how
in the storage of liquefied natural gases (LNG), which developed in the last
decades, driven by the petrochemical and space rocket industries. The technical
problems associated to the design of large cryogenic tankers, their construction
and safe operation have already been addressed and engineering problems have
been solved by the petrochemical industry. Cryogenic tankers of 200000 cubic
meters are in
operation and their
number in the world is estimated to be about 2000. LNG tankers are of
double-wall construction with efficient but non-vacuum insulation between the
walls. Large tankers are of low aspect ratio (height to width) and cylindrical
in design with a domed roof. Storage pressures in these tankers are very low.
Technodyne International Limited, UK , expert in the design of LNG tankers has
started a feasibility study in order to understand and clarify the issues
related to the operation of a large underground LAr detector.
Figure 54: Schematic layout of the inner detector of a future
Large Liquid Argon detector
Having in
mind the above considerations, a schematic layout of the inner detector is shown
in Figure 54, and the full detector is depicted in Figure 55. The detector is characterized by the large fiducial
volume of LAr included in a large tanker, with external dimensions of
approximately 40 m in height and 70 m in diameter. A cathode located at the
bottom of the inner tanker volume creates a drift electric field of 1 kV/cm over
a distance of about 20 m. In this field configuration ionization electrons are
moving upwards while ions are going downward. The electric field is delimited on
the sides of the tanker by field shaping electrodes. The tanker contains both
liquid and gas Argon phases at equilibrium. Since purity is a concern for very
long drifts of 20 m, one assumes that the inner detector could be operated in
bi-phase mode: drift electrons produced in the liquid phase are extracted from
the liquid into the gas phase with the help of a suitable electric field and
then amplified near the anodes. In order to amplify the extracted charge one can
consider various options: amplification near thin readout wires, GEM or LEM.
Studies in progress indicate that gain factors of 100-1000 are achievable in
pure Argon. Amplification operates in proportional mode. After a drift of 20 m
at 1 kV/cm, the electron cloud diffusion reaches approximately a size of 3 mm,
which corresponds to the envisaged readout pitch. If one assumes that the
operating electron lifetime is at least 2 ms (as obtained in ICARUS T600
detector during the technical run and better values of up to 10 ms were reached
on smaller prototypes during longer runs), one then expects an attenuation of a
factor 150 over the distance of 20 m, to be compensated by the proportional gain
at the anodes. The expected attenuation factor will not introduce any detection
inefficiency, given the nearly 18000 ionization electrons per 3 millimeter
produced along a MIP track in LAr. In addition to charge readout, one can place
PMTs around the inner surface of the tanker. Scintillation and Cerenkov light
can be readout independently. LAr is a very good scintillator with about 50000
/MeV. This light is distributed around a line at 128 nm and, therefore, a PMT
WLS coating is required. Cerenkov light from penetrating muon tracks has been
successfully within the ICARUS program; this much weaker radiation (about 700
/MeV between 160 nm and 600 nm) can be separately identified with PMTs without
WLS coating, since their efficiency for the VUV light is very
small.
Figure 55 : Artist view of a possible 100 kton liquid argon TPC.
A few
studies with the aim of identifying the main issues of the future systematic
R&D activities are in progress. Work is being conducted on the study of
suitable charge extraction, amplification and imaging devices, on the
understanding of charge collection under high pressure as expected for events
occurring at the bottom of the cryogenic tanker, on the realization of a 5 m
long detector column to simulate very long drift distances of up to about 20 m,
on the study of LAr TPC prototypes immersed in magnetic field, on the further
development of the industrial design of a large volume tanker able to operate
underground, and on the study of logistics, infrastructure and safety issues
related to underground sites.
In
particular, preliminary investigations are in progress with two generic
geographical configurations: a tunnel-access underground laboratory such as for
example the planned Frejus laboratories, and with a vertical mine-type-access
underground laboratory. Early considerations show that such sites correspond to
interesting complementary options. Concerning the provision of LAr, a dedicated,
not underground but nearby, air-liquefaction plant is foreseen. Technodyne
International has started investigating the technical requirements and
feasibility of such a facility.
Given the
extremely appealing physics potential of a large mass liquid Argon astroparticle
observatory, nucleon decay and neutrino detector, the community is invited to a
deep reflection concerning the feasibility of a next generation 100 kton LAr
TPC. In order to start up a complete program of investigations along these lines
of thoughts, it has been proposed the creation of an International Network of
colleagues and institutions interested in contributing to the development of
these ideas, which, if successful, could lead to a submission of Expressions of
Interest at a later stage in time.
If CERN
will decide to proceed with a high-intensity neutrino facility the realization
of a 100 kton LAr detector exploiting these beams could greatly benefit from a
strong CERN involvement at the level of the engineering, cryogenics,
infrastructure, test beams, and safety aspects, with CERN playing the role of
logistic center of gravity of the whole project.
7
Other particle physics
opportunities
7.1 Short baseline neutrino physics
(P.
Migliozzi)
7.1.1
Introduction
Over the past years
there has been a lot of interest in proposing new long baseline (LBL)neutrino
oscillation experiments with both conventional (pion and kaon decays) and
non-conventional (beta-beams and Neutrino Factories) neutrino beams. In this
context the proposal to study the detail of neutrino nucleon/nucleus
interactions with short baseline (SBL) experiments has been put forward
[Mangano01], [Bigi01], [Flemming04]. The motivations for a SBL program at the
future neutrino facilities can be summarized in two main streams: oscillation
physics and non oscillation physics. In the following we focus on the aspects
relevant to oscillations.
7.1.2
Oscillation physics
The next generation
of neutrino oscillation experiments [Apollonio02] aims at the precise
measurement of the elements of the neutrino oscillation matrix (PMNS) [PMNS].
There are two experimental techniques two perform this kind of measurements: the
appearance and the disappearance experiments.
In an appearance
experiment it is important to measure with high accuracy the transition
probability between two flavours (i.e. P(nm
®
nx)). The
experimental error on the measured oscillation probability can be written as
where Nfar
and Bfar
are the number of
observed events and the expected background at the far location, respectively;
Mfar
is the mass of the
detector at the far location; Fnm
the expected flux at
the far location; snx
is the cross-section
of the oscillated neutrino nx
and enx
its detection
ffciency. The variables dX
give the error on the
corresponding quantities.
The appearance
channels that will be exploited at future facilities to search for q13
and non-zero CP phase
are the 
and 
oscillations and
their CP or T conjugates. Indeed, while for the discovery of a non vanishing
q13
it is not mandatory,
although highly desirable, to reduce the impact of the intrinsic degeneracy on
the sensitivity, to search for CP violation in the leptonic sector one has to
measure the oscillation probability for both neutrinos and antineutrinos, and
then compare them to search for deviations from zero of the quantity
P(
) - P( 
).
In order to quantify
the relative contributions of the different terms to the overall uncertainty on
the oscillation probability we refer to the ne
appearance search
performed by the K2K experiment [AhnK2K04]. In K2K, that exploits a conventional
neutrino beam whose main component (nm) has an
average energy of about 1 GeV, the systematic error is ~30%, but
about 20% comes from the uncertainty on the cross-sections of the background
processes (mainly p0
and p±
production
in neutral-current neutrino interactions). This is due to the lack of data on
absolute inclusive NC single pion cross-sections as can be seen from Figure 56[Zeller03]. Almost all data on NC single pion
production exists in the form of NC/CC ratios and are summarized in Table 13. In some cases the experimental data may differ by as
much as factor of two or three. In Table 13[Zeller03] the predictions of the NUANCE Monte Carlo
are also shown and are in agreement with at least one of the
measurements.
Table 13 Measurements of NC/CC
single pion cross-section ratios. The Gargamelle data has been corrected to a
free nucleon ratio [Krenz78]. Also quoted are the free nucleons cross-section
predictions from NUANCE assuming mA = 1.032 GeV, mV =
0.84, and sin2qw = 0.2319 in each case.
* In their later paper [Derrick81], Derrick et al. remark that while this result
is 1.6_ smaller than their previous result [Barish74], the neutron background in
this case was better understood. ** The BNL NC p0 data was later reanalysed after properly taking into account
multi-pion backgrounds and found to have a larger fractional cross-section
[Nienaber].
The situation is even
more dramatic for antineutrinos where there are almost no data available. For a
complete collection of all available data on neutrino and antineutrino
cross-sections we refer to [Boone-web].
Figure 56 NC
1p
cross sections. Top
left: (nm
p
®
nm
p
p0); top right:
(nm
n
®
nm
n
p0);; bottom left:
(nm
p
®
nm
n
p+); bottom right:
(nm
n
®
nm
p
p-). Shown are the free
nucleon cross section predictions from NUANCE [Casper02] and NEUGEN [Gallager02]
with mA
=
1.032 GeV,
mV
=
0.84 GeV, and
sin2q
w
=
0.233.
Therefore, one of the
most important issue to be addressed at future facilities is the precise
measurement of neutrino and antineutrino cross-sections. In this respect, the
most suitable facilities to perform such a measurements are the b-beams and
the neutrino factories, where the neutrino flux can be predicted with an
accuracy of about 1% and 0.1%, respectively. However, waiting for the
construction of these facilities, there is an intense experimental program under
way with conventional neutrino beams (Mini-Boone; K2K, MINOS and T2K near
detectors; Minerna at NuMI)
whose aim, among many others, is to improve the present knowledge of
cross-sections.
7.1.3
Conclusion
Detailed study of
neutrino interactions is one of the most important topics to be addressed aiming
at a precise measurement of the elements of the neutrino oscillation matrix. As
an example, the impact of the error on the cross-sections on the determination
of the oscillation parameters Dm223
and q23
within the T2K
experiment (JHF®
SK with 5 years data
taking) is shown in Figure
57.
Figure 57 Sensitivity to
sin2qme
as a function of the exposure for
different estimates of the systematic errors [Itow01].
From the plot shown
in the top panel of Figure
58 it is also possible to have a feeling of the impact
of the cross-section accuracy on the sensitivity of future experiments
(5×JHF®
20×SK1
with 5 years data
taking) foreseen after the generation currently under construction and aiming at
the discovery of the CP violation in the leptonic sector. In order to improve
the sensitivity, the systematic error should be improved from the 10% foreseen
for T2K down to about 2%! Nowadays
it is about 30%. This gives an idea of the importance of an accurate
determination of neutrino cross-sections.
Figure 58 Dm2 atmospheric and sin2q23 determination at T2K by assuming present
systematic errors (left panel) and an improved scenario (right panel), figure taken
from [McGrew04].
7.2 High intensity muon physics
(A.Baldini,
A. Van der Schaaf)
A
community of physicists is proposing or performing experiments with low energy
muon beams. Among these items Charged Lepton Flavor Violation (CLFV) searches
have a long history reaching back 1948[Hinks48]. The absence of the µ®eg decay
has played a fundamental role in the construction of the Standard Model of
elementary particles physics. In the past 25 years the sensitivity to this decay
was raised by two orders of magnitude. The current best limit was given by the
MEGA experiment[Brooks99] which established a 90% C.L. limit of 1.210-11
for
the µ®eg branching
ratio (BR).
Grand
unified suspersymmetric (SUSY-GUT) theories, owing to the large top quark mass,
predict[Barbieri94] this decay to happen not much below the current experimental
limit. Figure
59 shows the SU(5) predictions for the
branching
ratio as a function of the right handed selectron mass and for several values of
tanb,
compared with the current experimental limit and
the aimed sensitivity of the MEG
experiment[MEG] at PSI. Recent indications from the combined LEP experiments
favor values of tanb
grater
than 10. Predictions for SO(10) could be about two orders of magnitude higher
than for SU(5).
Figure 59 Left: SUSY SU(5) predictions for the µ®eg branching ratio.
Right: Predictions
from a SUSY model including a see-saw mechanism for neutrino
masses generation (see text)
Another,
independent, source of CLFV in SYSY-GUT theories might come from neutrino
mixing. After the KAMLAND results the large mixing angle solution seems to
represent the best solution for the so-called “solar neutrino problem”. If a
mechanism of the see-saw type is introduced in SUSY-GUT theories to reproduce
the pattern of neutrino masses, sizeable contributions (of the same order of
magnitude or even higher than the ones discussed above) to the µ®eg process
take place[Hisano99] (see Figure
59). These contributions add up to the previous ones,
therefore making µ®eg
an extremely sensitive probe of SUSY-GUT theories.
It
must also be remarked that the µ®eg BR
due
to neutrino mixing alone would be completely unobservable (BR
»
10-54).
The detection of µ®eg
events
would thus be a clear, unambiguous sign of physics beyond the standard model,
even including neutrino masses.
Experimentally,
a beam of positive muons is stopped in a thin target and a search is made for a
back to back positron-photon couple with the right momenta and timing. The main
background in present experiments comes from the accidental coincidence of
independent positrons and photons within the resolutions of the used detectors.
The best available detectors for low energy positrons and photons must therefore
be employed. In the MEG experiment at PSI (see Figure
60) a surface muon beam with an intensity grater than
107
µ/s
will
be stopped in a thin target. A magnetic spectrometer, composed of a
superconducting magnet and drift chambers, will be used for the measurement of
the positrons trajectories. Positrons timing will be measured by an array of
scintillators. Photons will be detected by an innovative electromagnetic
calorimeter in which a total of about 800 photomultipliers will detect the light
produced by photons initiated showers in about 800 liters of liquid Xenon. In a
recent test at PSI the design energy resolution of 4.5% FWHM was obtained in a
100 l liquid Xenon prototype for 55 MeV photons.
The
aim of this experiment is to reach a sensitivity down to BR of the order
of 10-13,
with an improvement of two orders of magnitude with respect to the present
experimental limit. The start of the data taking is foreseen in 2006.
Figure 60 A
sketch of the MEG detector
Another
channel for CLFV investigation which is not limited by accidental background and
can therefore be used to improve the sensitivity to CLFV is muon to electron
(µe) conversion in nuclei. The ratio of the rate for this process with respect to µ®eg has been calculated by several authors, for various nuclei,
under assumptions on the relevant matrix elements which are valid in many SUSY
models (see Figure
61 [Kitao02]).
Figure 61
Computed ratio of BRµe/BRµ®eg.
Figure 62 Results
of the SINDRUM II experiment
Experimentally,
negative muons are brought to stop in a thin target and are subsequently
captured around a nucleus. The energy of a possible converted electron would be
equal to the rest muon mass minus the muon binding energy
(EB).
Two main sources of background are: i) beam correlated background due mainly to
radiative pion capture followed by g®
e+e-
conversions
and ii) electrons from muon decay in orbit (DIO). The first source of background
can be reduced by timing, the second one is intrinsic; DIO electrons spectrum
extends up to the energy region of electrons from µe
conversion
but with a spectrum proportional to (E
-EB)5.
An excellent electron momentum resolution is fundamental in order to keep this
background under control.
The
best experimental sensitivities to this process were obtained by the SINDRUM
experiment at PSI. Pion contamination in the beam was suppressed by means of a
moderator which exploited the different ranges of pions and muons. The final
result of the SINDRUM II experiment, which used a gold muon stopping target, is
shown in Figure
62. The DIO
electrons spectrum is well reproduced by simulations. Also shown is the
conversion signal for a 10-11BR.
The momentum resolution at the conversion peak is 2% FWHM. The 90% C.L. limit
established by the SINDRUMII experiment is 8·10-13.
The
MECO project at BNL (see Figure
63) plans to use a very intense (1011
µ/s)
pulsed muon beam for reaching a sensitivity to µe
conversion
down to BR »10-16.
The beam will be obtained by capturing most of the lower energy pions produced
in a target placed inside a superconducting solenoid magnet. Muons of suitable
momentum (60-120
MeV/c
) from pion decays are transported by a curved solenoid to the stopping
target and tracking system. The design electron momentum resolution, dominated
by interactions in the target is 900KeV FWHM. The pulsed structure of the beam
is indispensable to reduce the beam correlated background. A proton extinction
factor better than 10-9
between
two bursts must be obtained in order to reach a sensitivity to BR
£
10-16.
In
the PRISM/PRIME project at J-PARC the same muon production scheme as MECO is
adopted. After pion production in a solenoid the beam is transported in a
circular system of magnets and RF cavities (FFAG ring) which acts as a pion
decay section (increasing beam cleaning) and reduces the muon energy spread. The
features of this beam would be an extremely high intensity (1012
/s)
of clean muons of low momentum
(
»70MeV/c)
with a narrow energy spread (few % FWHM). The last feature is essential to stop
enough muons in thin targets. If the electron momentum resolution will be kept
below 350 KeV/c
(FWHM) the experiment will be sensitive to µe
conversion
down to BR £
10-18.
The
SPL could be used to produce very intense muon beams. Preliminary estimates
obtained by suitably scaling MECO calculations indicate that >1012
µ/s
stopped
muons and a pulsed structure suitable for performing a very sensitive
µe
conversion experiment (down to BR <
10-18
or
better) could be obtained. On the contrary a continuous muon beam seems more
difficult to be realized. Other very interesting kinds of experiments, apart
from CLFV, could be performed by using a very intense low energy muon beam.
These include precise measurements of the muon decay parameters, measurement of
the muon anomalous magnetic moment and of the muon electric dipole moment. The
muon beams characteristics needed by all the different kinds of experiments were
investigated some time ago by the CERN stopped muons working group and are
reported in [Aysto01].
7.3
Physics at Higher Intensity PS or
SPS at CERN
(A. Ceccucci)
The strategic goals of CERN must
include the exploitation of the PS and SPS machines that will be employed as
injectors of the LHC just for 15% of the time. It is important to distinguish
between two scenarios:
Short to Medium Term: assume the
current PS and SPS with adyabatic increase --always welcome!-- of the delivered
proton intensities up to a factor of two. As outlined in [Cappi:2001au] bigger
gains are unrealistic even with an SPL because large PS and SPS collective
effects are the essential limitations.
Longer Term: the path toward
higher LHC luminosity is to foresee a new injector chain capable to deliver
significant higher intensities at high energy. To employ significantly larger
proton intensities at fixed target, the extraction and the targets need to be
refurbished as well.
Let us focus here on one example:
the opportunity to use the current SPS to perform crucial tests of the Standard
Model (SM) by measuring kaon rare decays for which very clean theoretical
predictions are available [Buchalla98ba]. The most interesting are:
, and
, which is a CP violating process.
The measurement of the Branching
Ratio of 
is the cleanest
way to measure |Vtd|, while the measurement of 
would provide the cleanest measure of the
CP-Violation predicted in the SM. The importance of these decays is that the
hadronic matrix elements are well measured from the Kaon semi-leptonic decays.
In addition, the remaining uncertainties are largely parametric in nature and
will decrease to become negligible once the uncertainties due to other CKM
parameters will be reduced.
Experimental progress on
has been impressive over the past
three decades: the BNL experiment 787 has published evidence for two events
[Adler01xv], and the subsequent experiment 949 has claimed a third event
[Anisimovsky04hr]. These experiments exploit the large amount of protons
available from the 24 GeV AGS to study kaon decays at rest. To test the precise
prediction of the SM however, one should aim to collect hundreds of such events, which is extremely
difficult with stopped kaon experiments.
Enticed by the quality of the
secondary beams prepared for the charged kaon experiment (NA48/2), the NA48
Collaboration has realized that a very competitive programme to study
can start as soon as the SPS will resume
operations after the commissioning of the LHC. The parameters of the possible
future beam compared to the present ones are given in Table 14. It is noteworthy that by using the already available
3 1012 protons on the T4
target, the experiment would be able to collect 40 times the kaon flux of
NA48/2.
Table 14 Comparison between the current NA48/2 beam and the future one. The figures in brackets in the last column refer to increase in rate with respect to the sum of the positive and negative NA48/2 beams
The study of 
is not limited by the
availability of protons from the current SPS. Although the experiment requires a
long spill which is in competition with the CNGS programme, this is regarded as
a scheduling issue rather than a technical one. A feasibility study for an experiment
able to collect at least 50 
events with a signal to background ratio
of ~10:1 in about two years of data taking (NA48/3) has been performed. The two
undetectable neutrinos in the final state require the design of an experiment
with redundant measurement of the event kinematics and hermetic vetoes to
achieve the necessary background rejection. Particular care has to be taken to
suppress the two body decays 
and 
which have Branching Ratios up to
1010 times larger than the expected signal. The reconstruction of the
two body kinematics cannot be completely exempt from reconstruction tails and
backgrounds can originate if photons from 
are not detected or if muons from
are mis-identified as pions. To
suppress backgrounds from the two body decays, kinematics and particle
identification have to be used in conjunction. Only in the absence of
correlations the rejection power obtainable applying the two techniques together
will equal the product of the single rejection powers. The advantage of using
400 GeV/c protons from the SPS to
perform the experiment is two-fold:
on the one side, the cross-sections to produce kaons increases as a function of
proton energy so that to achieve
the same kaon flux one needs less protons
thus reducing the non-kaon-related accidental activity. In addition, the higher
kaon energy leads to easier photon detection which simplifies the suppression of
the backgrounds originating from 
. For example, employing a 75
GeV/c kaon beam and limiting the momentum of the reconstructed p+
to 40
GeV/c, there are at least 35 GeV of electro-magnetic energy from the
p0 deposited into the
photon vetoes. This reduces significantly the probability that both photons are
left undetected because of photonuclear reactions.
The disadvantage of employing high
energy protons and, consequently, high energy secondary beams, is that the pions and the protons cannot be
efficiently separated from kaons.
The consequence is that the upstream detectors which measure the momentum and the direction of the kaons
are exposed to a particle flux
about 17 times larger than the useful (kaon) one. It is important to point out that the detectors placed
downstream of the decay region do
not suffer from the same limitation because:
- The protons and the undecayed
kaons and pions are kept in a vacumm beam-pipe that crosses the downstream
detectors.
- The muons from pion decays stay
in the beam-pipe without illuminating the drift chambers because of the small
transverse momentum released by the pion decay.
In the longer term, a 1 MW and
high-energy proton beam would be ideal to consider also a very competitive
programme addressing 
, the so called holy grail of
kaon physics. More details can be found in the Expression of Interest
[NA48EOI04] submitted by the NA48 Collaboration.
8
Nuclear physics
8.1 The future of nuclear physics studies
(P.
Butler, W. Gelletly)
The study of atomic nuclei lies in the mainstream of modern physics. It is closely allied to studies of other finite N, many-body systems such as quantum dots, metallic clusters, grains, fermion condensates etc. Although they are mostly nanostructures and nuclei are femtostructures they have many common features including shell structure, collective modes of motion and pairing. Each of these systems has unique features. Nuclei present a two-fluid(protons and neutrons), strongly interacting system that has many degrees of freedom. It is difficult to study but the tools to do so are well developed.
All of these
systems reflect two of the main themes of modern physics, namely “How can such
complex systems be built from a few, basic entities?” and “Despite the
complexity how do we understand the surprisingly simple excitation patterns and
symmetries they exhibit?” Theoretical understanding of each of these systems
will impinge strongly on our answers to these questions in all of these systems.
Nuclear physics is also closely related to particle physics and astrophysics and
has many applications.
There are many specific
challenges in nuclear structure physics:
a)
Firstly we do not know the
limits of nuclear existence. In particular we do not know what is the heaviest
element we can make and we have only a vague idea of where the neutron drip-line
lies. In the former case we have evidence that there is an island of superheavy
nuclei, established by the extra binding from the shell structure. However with
stable beams, even with long-lived, radioactive, actinide targets, we can only
create species many neutrons away from the epicentre. In the latter case our
best estimates of where the neutron drip-line lies are based on mass formulae.
These formulae all agree where we have measured masses but disagree by some
20-30 neutrons in where they put the drip-line for an element such as Sn(Z =
50).
b)
Secondly we observe
dynamical symmetries in nuclei. In terms of the Interacting Boson Model(where
pairs of nucleons are treated as bosons) nuclei can be classified in terms of
limiting dynamical symmetries corresponding to a spherical vibrator, a gamma
soft rotor and an axially symmetric deformed rotor. Almost all even-even nuclei
are at these limits or lie between them. Recently Iachello has also introduced
the idea of phase transitions between the limits and examples of nuclei close to
the critical points have been found. One key question is whether these dynamical
symmetries will persist in nuclei far from stability and, in particular, will
the new “critical point symmetries” persist there? In addition, in nuclei with a neutron
skin will one see dynamical symmetries associated with a two-fluid system
consisting of a proton-neutron core and the neutron skin?
c)
Pairing is important in
nuclei. For example it dictates the fact that 4,6,8He are bound and
5,7He are unbound. In nuclei we are faced with the possibility that
we can have isoscalar and isovector pairs of neutrons and protons. This may
manifest itself in terms of either n-p or alpha condensates in N = Z nuclei.
This is likely to be the only regime where the isoscalar component manifests
itself since elsewhere it will be swamped by like pairs.
d)
In nuclei far from
stability, particularly in the neutron-rich nuclei, the density will be low near
the nuclear surface. One question of considerable importance is how important
pairing is in such a low-density environment.
e)
Atomic nuclei exhibit a wide
variety of types of excitation that range from single and multi-particle
excitations to a variety of collective modes. These include rotations,
vibrations of various types and so-called giant resonances in which the neutron
and proton fluids oscillate relative to one another. Another key question is
whether we will observe new types of oscillation far from stability. We might
anticipate a scissors –like motion of a deformed core against a neutron skin or
even an oscillation of separate neutron and proton fluids relative to the skin.
In addition we might expect a pygmy resonance, a simple vibration of core and
neutron surface.
f)
Underpinning much of our
understanding and theoretical interpretation of nuclear structure is the shell
structure. This was first seen in atoms and nuclei but , more recently , it has
been observed in metallic clusters and quantum dots as well. In simple terms one
can define the shell structure as being due to the bunching of levels in the
system, which leads to the shell gaps and its consequences. The well known shell
gaps in stable nuclei are the result of the poorly understood l.s
interaction. In recent years it has become apparent that the shell structure is
a very flexible concept and that the gaps vary both with rotational frequency
and isospin. As we move away from stability on the neutron-rich side the surface
density falls since the neutrons lie close to the top of the potential well. As
a result we expect the l.s
interaction to weaken and with it the shell structure. Since the shell structure
dictates much of what we see in nuclei it is vital that we are able to map out
this underlying structure far from stability. This challenge can be summed up as
“How does the shell structure change with a large neutron
excess?”
To answer all of these
questions we require high quality, intense beams of radioactive ions. We also
need new instruments and techniques to allow us to take advantage of the beams.
Multi-MW driver accelerators will be vital to create this opportunity and are
the key to producing the beams of radioactive nuclei we
need.
8.2 Nuclear dynamics and the nuclear equation of state
(F. Gulminelli)
8.2.1 State of the art
Our knowledge on the nuclear Equation of States and nuclear thermodynamics has considerably progressed in the past twenty years. Exclusive analyses of multifragmentation data, measured with low threshold and high granularity second generation 4p detectors, have been performed. These studies have lead to a consistent bunch of circumstantial evidences of a transition from a bound and ordered liquid-like phase, to an unbound and disordered gas-like phase of light clusters and nucleons. A spectacular scaling of the distribution of fragment sizes has been observed [Elliot02] and a thermodynamically consistent set of critical exponents has been extracted, in agreement with the liquid-gas universality class. A systematic comparison of different thermometers has shown that the multifragmentation phenomenon takes place at a characteristic temperature that has been interpreted as the transition temperature of a nuclear liquid-gas phase transition [Natowitz02]. Large fluctuations of the fragment partitions have been reported [Schrenberg01,D’Agostino04]. that correspond to huge configurational energy fluctuations overcoming the value expected for a canonical ensemble of loosely interacting fermion clusters (Figure 64, left side). If the fragmenting nucleus is close to a thermodynamic equilibrium, this fluctuation signal can be converted into a heat capacity [Dauxois02]. Then, the abnormally large fluctuations would indicate a negative heat capacity between two divergencies, with an amplitude in energy related to the latent heat of the transition (Figure 64, right side). If confirmed, this signal represents a quantitative measurement of the nuclear phase diagram and the first measurement of a negative heat capacity in a mesoscopic system. To confirm the negative heat capacity and settle the finite temperature equation of state, a complete detection on a 4p geometry of the masses and charges of all the reaction products is mandatory. Indeed the limited isotopic resolution of present apparatus induces a dispersion in the calorimetric determination of the deposited excitation energy, which in turn affects the fluctuation measurement with a systematic error which can presently only be estimated through simulations in a model dependent way. Moreover, a full isotopic resolution is necessary to constrain the statistical models and determine the degree of equilibration of the transient nuclear source. A device adapted to nuclear matter studies (FAZIA) has been recently proposed [EURISOLE] and the R&D is taken in charge by the European collaboration AZ4p.
The adequacy of this
project has been recognized in the last NuPECC report [NUPECCLRP].
Figure 64 Left side: normalized
configurational energy fluctuations and canonical reference (dark grey) measured
in peripheral Au+Au collisions at 35 A.MeV (light grey), and central collisions
of an Au beam on different targets (symbols). Abnormally high fluctuations are
observed in the energy range 2<E*/A<6.5. Right side:
corresponding heat capacity deduced in the framework of thermodynamic
equilibrium. All data are from the Multics-Miniball collaboration
[Schrenberg01],[D’Agostino04]
8.2.2 The perspectives of exotic beams
A new high performance RIB facility will offer the possibility to study the role of the isospin (N/Z ratio) in dynamical and statistical de-excitations of hot nuclei. This search will probe the dependence of the nuclear equation of states on the isospin terms under compressed, normal and dilute conditions. The isospin dependent phase diagram of nuclear matter is largely unknown. At zero temperature, the density dependence of the symmetry energy is the subject of numerous theoretical investigations [Greco03]. To constrain the huge theoretical uncertainties on this quantity, isospin diffusion experiments are needed with beam energies in the range 30-100 A.MeV and a large panel of isotopes around A=100 ] [Tsang04]. At finite temperature, the extra dimension provided by the isospin degree of freedom in the nuclear phase diagram (Figure 65, left part) leads to the expectation of different new phenomena that could be experimentally probed. For the fragmentation of proton rich nuclei, the transition temperature is expected to dramatically decrease approaching the proton drip line [Bonche85], and theory predicts that the first order phase transition should become a cross over due to the Coulomb interaction [Gulminelli03].
The phenomenon of isospin distillation is expected in the fragmentation of neutron rich nuclei [Mueller95], which can be experimentally investigated from the production yield of different isotopes (Figure 65, right side). In both cases beam energies in the range 20-100 A.MeV are needed, as well as a new high resolution 4p device: the FAZIA concept recently proposed in the instrumentation report of the EURISOL Key Experiment Task Group [EURISOLE] (see above).
Figure 65 left side: theoretical prediction for the coexistence zone of asymmetric nuclear matter as a function of proton and neutron density from ref. [Mueller95]]. Right side: relative production yield of light isobars (gas phase) as a function of temperature from ref. [Chomaz99]. A neutron enrichment (upper line) is predicted for this neutron rich hot nucleus (160 neutrons and 96 protons) respect to the simple combinatorial expectation (lower line).
8.2.3 Conclusions
The study of the de-excitation pattern of hot nuclei produced in heavy ion collisions constitutes a unique opportunity to probe the interdisciplinary thermodynamics of mesoscopic systems and look for exotic phenomena as negative susceptibility and negative heat capacity [Dauxois02]. If many experimental data already exist on the fragmentation of stable nuclei, almost nothing is experimentally known about the thermodynamics of strongly asymmetric nuclear matter. These studies do not only aim to quantitatively understand the phase diagram of finite nuclei, but also bear important information on the thermodynamics of dense matter and stars [Glendenning01].
To perform these analyses, exotic beams both on the proton and on the neutron rich side are needed in the energy region of 30-100 A.MeV, as they could be produced by the EURISOL facility.
8.3 Astrophysics with R.I.B.
(K.-L.
Kratz)
As outlined in the recent
NuPECC report on ‘Nuclei in the Universe’ [NUPECCLRP], nuclear astrophysics has
developed in the last decades into an important interdisciplinary sub-field of
‘applied’ nuclear physics. To the nuclear physicist many phenomena in the
universe represent nuclear experiments on a grand scale, often under conditions
that – at least for the time being - cannot be replicated on earth. To the
astrophysicist nuclear physics represents experimental and theoretical sources
of data which are needed to model astronomical observations of many
astrophysical scenarios. Examples of this dichotomy are the explanation of the
energy production in explosive thermonuclear burning and the postulation of two
distinct neutron-capture processes as the origin of the heavy nuclei beyond
iron.
Among the most interesting
applications of explosive nucleosynthesis scenarios in binary systems are novae
and X-ray bursters. Novae are in fact thermonuclear explosions on the surface of
a white dwarf accreting matter from a companion star. Once the white dwarf’s
freshly accreted surface layer reaches a critical density and temperature,
nuclear reactions trigger a thermonuclear runaway. The explosive burning of
hydrogen and the decay of freshly synthesized proton-rich nuclei provide the
energy that leads to the observation of a dramatic brightening of the
star.
X-ray bursters are believed to be neutron stars accreting material from a low-mass companion star. In regular or irregular intervals of typically 1 hour to 1 day, the accreted layer ignites and a thermonuclear runaway evolves burning hydrogen and helium within tens of seconds. The respective nucleosynthesis process is today known as the rapid proton-capture process, i.e. the rp-process. Provided that a sufficiently high mass-loss out of the gravitational potential of the neutron star is possible, X-ray bursts may contribute to the galactic nucleosynthesis of light (proton-rich) p-nuclei [Wiescher98,Schatz98]
Figure 66 shows the full sequence of nuclear reactions powering
a ‘normal’ X-ray burst, calculated with a one-zone model coupled to a complete
reaction network [Schatz01]. The
endpoint of the
rp-process is expected in the Sn-Sb-Te region, where a reaction cycle is formed
as a consequence of low a-binding energies of the
proton-rich Te isotopes. This Sn-Sb-Te cycle prevents the synthesis of nuclei
heavier than A ≈ 106 in the rp-process.
Figure 66 Time integrated reaction flow for a complete X-ray burst. The thermonuclear runaway is triggered by the 3 a-reaction and the break-out reactions of the hot CNO cycle into the ap-process, which provides the seed for the hydrogen burning via the rp-process. The inset shows the Sn-Sb-Te cycle in detail. For more details, see reference [Schatz01].
Summarising the nuclear-data needs for
X-ray burst calculations, the most important parameters are nuclear masses
(including p-separation energies) near the proton drip-line, b-decay half-lives along the
process paths (in some cases including decay from excited and isomeric states)
and p-capture rates on ‘short-lived’ nuclei (in particular those within
so-called 2p-capture sequences [Schatz98]).
The understanding that the
existence of the heavy elements in nature is due to neutron capture is almost
half a century old [Burbidge57, Cameron57, Coryell61] . The abundance features of solar system matter
[Anders89, Lodders03] beyond Fe are seen to be
correlated with the positions of the neutron shell closures at N=50, 82
and 126. The splitting of the abundance peaks in the mass regions A ≈ 80,
130 and 195 (see Figure
67) in fact reveals signatures of (at least) two types
of neutron-capture processes with quite different astrophysical
environments.
1.
A process with small
neutron densities experiences long neutron-capture time-scales in comparison to
b-decays
tb< tn,g ): slow neutron capture, the s-process, causes abundance peaks in the flow path at nuclei with
small neutron-capture cross sections, i.e. stable nuclei with magic neutron
numbers [Kappeler98].
2.
A process with high neutron densities
and temperatures experiences rapid neutron capture and the reverse
photodisintegration with tn,g , tn,n < tb: the r-process causes
abundance peaks due to ‘long’ b-decay half-lives where the flow path comes closest to stability.
This occurs again for magic neutron numbers, but for far-unstable nuclei
[Kratz00].
Figure 67 Schematic curve of
Solar-System abundances as a function of atomic weight, based on the 1956 data
of Suess and Urey ] [Suess56].
Approximately half of the nuclear species in nature beyond iron are produced via neutron captures on very short time scales in neutron-rich environments, i.e. the so-called r-process. Only under such conditions is it possible that highly unstable nuclei near the neutron drip-line are produced, also leading – after decay back to stability – to the formation of the heaviest elements in nature like Th, U and Pu. Far from stability, magic neutron numbers are encountered for smaller Z and A numbers than under the low neutron-density s-process conditions in the valley of b-stability. Despite its importance, the exact stellar site where the r-process occurs is still a mystery. However, two astrophysical settings are suggested most frequently, (i) type II supernovae (SN II) with postulated high-entropy ejecta (see, e.g. [Woosley94, Freiburg99]), and (ii) neutron-star mergers or similar events (like axial jets in SN explosions) which eject NS matter with low entropies (see, e.g. [Lattimer77, Rosswog00]). The key to its understanding will probably only be obtained from a close interaction between astronomy, cosmochemistry, nuclear physics and astrophysical modelling of explosive scenarios.
To illustrate the present unsatisfactory
situation, with the use of different mass models differences in the main waiting
point behaviour around the N=82 closed shell can be deduced, as shown in
Figure
68. Using masses from ‘unquenched’ models such as FRDM
or ETFSI-1, the N=82 closed shell is very abrupt and the neutron captures
proceed quickly to the N=82 nuclei at low Z. Consequently, very
few nuclei with more than 10% abundance in a given isotopic chain are found
before reaching the neutron closed-shell N=82 (Figure
68, top left in the circled area). This feature is
responsible for the trough (Figure
68, top right) in the fit of the abundance curve of the
r-elements at A~120 since very few r-progenitors are found at this mass
number.
Figure 68 3 (Left:) The r-process waiting points for mass models with strong neutron shell closures (such as FRDM or ETFSI-1) are shown in the vicinity of the neutron shell closure at N=82 for a neutron density of nn=9.5×1020 cm-3 and a temperature of 1.2 ×109K. Nuclei with more than 10% of the population of an isotopic chain are represented with an open square. Open squares with a cross indicate waiting-point nuclei with the maximum abundance in an isotopic chain. The nuclei in the valley of stability are displayed as full squares. The bottom part shows the expected waiting points using the masses close to N=82 from models which contain shell quenching (such as HFB/SkP or ETFSI-Q). It is shown that the region within the circle at Z≈40, A≈78 contains more progenitors [Pfeiffer96]. (Right:) Comparison of calculated abundances with the Nr,Θ distribution for ‘unquenched’ (top) and ‘quenched’ masses (bottom).
On other hand, calculations performed
within the HFB/SkP or the ETFSI-Q models showed that the N=82 closed
shell is substantially ‘quenched’ at very neutron-rich heavy nuclei. This
creates r-progenitors already before reaching the N=82 closed-shell.
Using these masses, the A~120 trough is filled, in closer agreement with
the Nr,Θ curve. This emphasises that a better knowledge of
nuclear properties is required when approaching the major closed shells far from
stability, for both nuclear physics and astrophysics, in order to see if these
shell gaps are, indeed, quenched. For example, if shell quenching far from
stability would turn out to be pronounced, the classical N=82 shell gap
should steadily decrease below doubly-magic 132Sn and eventually
vanish at 122Zr. Then, 122Zr would no longer act as an
r-process waiting point. Instead, a new (semi-) doubly-magic zirconium isotope
with an N=70 shell closure, i.e. 110Zr, might be expected (see
references [Pfeiffer01, Pfeiffer96]), which then would replace 122Zr
as waiting point. Such a change in shell structure would have dramatic
consequences on all r-process relevant nuclear physics parameters. For example
the (predicted) T1/2 and Pn values of
110Zr would change by an order of magnitude from an ‘unquenched’
deformed to a ‘quenched’ spherical ground-state shape. Experimental studies of
this shell quenching at large N/Z not only along N=82, but
also for N=50 and N=126 are therefore major
challenges.
For instance, the study of
78Ni, hitherto produced at a rate of few nuclei per week, constitutes
an important landmark for the study of the N=50 shell-closure. This will
show whether current theoretical approaches as macroscopic-microscopic models,
self-consistent microscopic theories, and relativistic mean-field theories can
really predict the influence of the large neutron excesses and the possible
modification of shells due to proton-neutron interactions. In the N=82
region, mass measurements should extend below Z=48 in order to confirm
the shell quenching recently observed for 130Cd. [Dillmann04].
Therefore, the study of the refractory elements Pd, Rh and down to Tc or even Zr
is of utmost importance (see Figure
69). The study of the N=126 closed shell is far
from being attainable right now with either existing or future short-term
facilities.
Figure 69 Limits of experimentally determined masses in the neutron-rich closed-shell regions N=50, 82 and 126.
8.4 Fundamental symmetries and interactions
(K. Jungmann)
Symmetries play a key role in physics.
Whereas local symmetries correspond to forces, global symmetries are associated
with conservation laws. A number of conservation laws exist where an underlying
symmetry could not yet be identified and which therefore have no status in
modern physics. Among those are the conservation of electric charge, lepton and
baryon number, charged lepton number. They are consequently among the not
explained features in the Standard model which otherwise is an excellent
description of all observations to date in particle physics. Other mysteries
remaining in standard theory are the origin of CP violation, the apparent
dominance of matter over anti-matter in the universe. Most intriguing is the
fact of three particle generations with the observed mass hierarchy. A
Multi-Megawatt Proton machine would open up opportunities to conduct experiments
to shine light into such fundamental questions in physics.
An
international working group charged by NuPECC [NUPECCLRP] has identified the possibilities
for contributing to solving urgent scientific questions of fundamental nature
using nuclear physics techniques and typical nuclear physics equipment. A large
number of these possibilities turned out to be best performed at a high power
Proton Driver facility. This arise from the fact that many experiments performed
until today are statistics limited and would enormously benefit from high
particle numbers (neutrinos, radioactive isotopes, muons, pions, Kaons , cold
neutrons and antiprotons). Some most promising possible experiments to make
progress in understanding nature are listed in Table 15. The table gives further the preference for a low (~1
GeV) or high ( ~30 GeV) energy facility.
In the
field of neutrino physics (besides direct searches for a finite mass in
non-accelerator spectrometer experiments) the confirmation of oscillations and
the search for CP-violation in the lepton sector require long base line
experiments. Here intense beams are indispensable. The time before they become
available may be well spent exploring novel detector techniques, in particular
such using large mass natural salt domes or directional sensitivity at low
energies or even air showers.
Time
reversal (T) respectively CP violation may relate to the matter-antimatter
asymmetry in the universe. The search for permanent electric dipole moments (EDMs) of electrons, nucleons, nuclei,
atoms, molecules and second generation particles such as the muon all have an
independent potential contribute in a unique way to understanding T and CP
symmetry violations. The full nature can only be assessed using several systems.
Particular interesting systems are Radium atoms due to both possible atomic
enhancement for an electron EDM and nuclear enhancement of a nucleon EDM due to
close lying states of opposite parity. A novel scheme using charged relativistic
particles in a magnetic storage ring will allow a sensitive muon EDM experiment.
The advantage of the muon is apparent in models beyond standard theory with
nonlinear mass scaling. Conceptually the muon as a second generation particle
may be sensitive to other CP -violating mechanisms than the first generation. A
further approach to T-violation is possible through neutrino- b-particle correlations in nuclear
b-decay.
For rare
and forbidden decays the charged lepton family conservation remains a law
without standing in modern physics, as no underlying symmetry has been
identified yet. The sensitivity to predictions of speculative models is large,
particularly since the experimental detection limits can be lowered
significantly with strongly enhanced particle fluxes at a Multi-Megawatt
facility.
New weak
interaction types (other than V-A) can be searched for in trapped radioactive
atom decays. Here both advanced trapping techniques and sufficient nuclei are
the key issues. A large number of nuclei is also required for careful systematic
studies.
The
unitarity of the Cabbibo-Kobayashi-Maskawa matrix is required by standard
theory. A deviation may relate to more than three particle generations. At
present the most urgent experimental input is required from strange particle
(kaon) decay to determine Vus. On the long run a renewed pion
b-decay experiment would be the
cleanest approach towards Vud , because of the by far best understood
associated theory of hadron structure as compared to, e.g. nuclear
decays.
The
conservation of CPT is most fundamentally assumed in most physics models. A
severe test is therefore rather important. New models suggest to search for
interactions rather than relative numbers in comparing particle and antiparticle
properties. Only interactions are relevant in physics. These test come
parasitically with muon or antiproton experiments, e.g. through searches for
diurnal variations in measured quantities.
Nuclear physics and nuclear techniques offer a variety of possibilities to investigate fundamental symmetries in physics. The advantage of high particle fluxes at a Multi-Megawatt facility allow higher sensitivity to rare processes because of higher statistics and because in part novel experimental approaches are enabled by the combination of particle number and suited time structure of the beam.
Table 15 Physics possibilities at a Multi-Megawatt Proton Driver. Most experiments would benefit from a pulsed time structure of the beam.
|
Physics
Topic |
Physics
question to
address |
Method |
Comments |
Preferred
Energy | |
|
~ 1GeV |
~30GeV | ||||
|
The Nature of
Neutrinos
|
Oscillations
, CP viol Masses
|
Long baseline spectrometer |
Novel detectors? Salt
domes? Only nm |
´
´ -
´ | |
|
T
and CP Violation |
Permanent
electric dipole moments D (R) coeff. in
b-decays D0-
decay |
Spin precession in electric
fields; Trapping of radioactive
atoms |
Novel method using
rings Radium
isotopes Stored radioactive
atoms Antii-proton
facility |
´
´ ´
´
´ | |
|
Rare and
Forbidden Decays |
n-nbar
conversion M-Mbar
conversion
m®eg m
®3e m
N®
N e convers. |
Dedicated
spectrometers |
Ultracold
neutrons Novel
method possible,unique potential Unique
potential Unique
potential Unique
potential |
´
´
´
´
´
| |
|
Correlations
in b-decay
|
Non
V-A in
b-decay |
radioactive
nuclear decays |
Optically trapped radioactive
atoms |
´
´
| |
|
Unitarity
of CKM-Matrix |
n-decay p-b
decay (super allowed b-decays),
K-decays |
Lifetimes and transition
probabilities |
Great potential to
test Physics beyond
SM, Presently mess in Vus
, |
´
´
´
-
´ | |
|
CPT
Conservation |
N p m |
Diurnal Variations of spin
dependent quantities |
Interaction based models
needed |
´
-
´ ´
´ | |
8.5 New approaches to the study of the nucleus with muons and antiprotons
(J. Aystö)
The trend within nuclear structure physics is to take the many-body system of nucleon that consists the nucleus to its extremes. Here, varying the isospin parameter is a crucial path in deepening our understanding of atomic nuclei. Furthermore, important astrophysical processes often involve nuclei very far from stability. Thus, there is a general consensus [nupec03] that the prime emphasis of future nuclear structure physics will lay on experiments with radioactive beams, and in particular the forthcoming second-generation facilities like the planned facility at GSI [gsi02] and EURISOL [euris03] in Europe. These facilities will be able to deliver several orders of magnitude higher intensities of radioactive beams than today while simultaneously move the experimental frontier several isotopes further toward the driplines. However, there are possibly further synergies that could be exploited at an advanced ISOL-facility since the very intense proton driver beam of several mA will simultaneously be able to produce copious amounts of pions and muons; a physics programme utilizing these has been outlined in [Aysto01].
The processes involved in formation of muonic atoms and decay determine the experimental physics observables; in the capture of a muon in an atomic orbit, the de-excitation process will take place through emission of muonic X-rays that probe the nuclear charge distribution. Subsequently, a sizable part of the muonic atoms will undergo the weak process of muon capture
ZXN + m ®
Z-1YN+1 + nm
This semi-leptonic process has a positive Q-value of »100 MeV and thus populates highly excited states in the daughter nucleus, also at high multipoles. For neutron-rich nuclides, it has the additional attractive feature that the resulting system is one step further away from the line of stability. The physics that could be addressed by combining RIBs and muons is diverse, and in some cases hard to attain experimentally by other methods. In addition to nuclear structure issues, muon capture involves largely the same matrix elements as in neutrino scattering. Thus, muon capture rates can constrain cross-sections and are of astrophysical interest.
A possible key experiment could be to study highly excited states in the doubly-magic nucleus 78Ni through muon capture on 78Cu. 78Cu can already now be produced with the intensity of several hundred atoms/s at ISOLDE [turrion03] whereas 78Ni is considerably harder to produce and would need at least 103 atoms/s to permit e.g. studies of the lowest excited states through Coulomb excitation. The situation could be much more favorable for muonic atoms; Figure 70 shows an RPA calculation shows that the majority of muonic 78Cu will populate states in 78Ni through muon capture, reaching beyond the neutron separation threshold. Only 14% are lost through muon decay. Combining this with a shell model calculation to estimate the capture rate to bound states yields a branching of 37% to these. It should be noted that this estimate is less robust than the total capture rate since the ground state spin of 78Cu is unknown and the neutron separation energy in 78Ni is taken from systematics. The possibility to tag the muon capture process by observation of gamma transitions in the created nucleus has been used extensively in experiments on stable nuclei; a recent example concerning 48Ca can be found in [fynbo03].
Figure 70 Feeding of excited states in 78Ni by muon capture on muonic 78Cu according to RPA calculations.
Experimentally, it is very challenging to merge the relatively weak intensities of exotic nuclei with the short-lived (t = 2.2 ms) muons. However, cyclotron traps have been successfully operated to obtain low-energy muon beams [dececco97] at PSI and the recent advances in e.g. formation of anti-hydrogen in traps [gabrielse02] has shown that a nested trap could be a feasible approach provided that sufficient muon and ion densities can be reached. An estimate of the formation rate based on scaling the performance of contemporary devices has been made, leading to the formation of ~(101 - 102) [jungmann] radioactive muonic atoms/s [2]. Merging beams of ions and muons in storage rings is a possible approach, however the short muon lifetime limits the number of merging passes. For a possible design of nested storage rings for RIB and exotic probes see [lindroos04]. Currently, the most promising concept involves stopping muons and ions in cryogenic fluids. A concept of thus stopping and subsequent transfer muons in liquid hydrogen and deuterium layers to implanted ions has been developed [strasser99]. Recently, there has been major progress in this approach [strasser04]. The similar concept of stopping and transporting radioactive ions in superfluid helium was recently experimentally demonstrated with good efficiency [huang03].
The ‘common knowledge’ that the ISOL-method has severe drawbacks due to the decay losses in the target-ion source system when trying to study very short-lived species does not remain valid if beam quality becomes an issue. This is clearly the case for the methods outlined here, where emittance and energy spread become crucial obstacles for the formation of muonic atoms, as well as for existing tools for RIBs like collinear LASER spectroscopy or possible future tools like electron-ion scattering [gsi02] or anti-protonic atoms [euris03]. A high-energy beam from a fragmentation facility needs to be cooled (stochastic and subsequently electron cooling) and possibly decelerated in several time-consuming steps, limiting the experimental scope to halflifes of the order of seconds. The ISOL-method, however, produces a beam which directly from the ion source has good properties, and experience with Penning trap and RFQ coolers show that substantial improvement can be reached in a few tens of milliseconds. Thus, unless alternative methods are shown to work for intense high-energy radioactive beams, the ISOL-method occurs to have the best potential concerning new experimental probes where the beam intensity is crucial. See Figure 72
Figure 71 Experimental reach expressed in beam energy and halflives for
``hot'' (directly following production) and ``cold'' (following improvements of
beam properties) beams from ISOL-type and in-flight facilities.
9 Conclusions and outlook
9.1 Accelerators
(B. Weng)
There is a world-wide surge of interest in the design and applications of High Power Proton Accelerators. Their use ranges from neutrino super beam, muon colliders, Beta-beam, double beta decay, radioactive ion beam, to spallation neutron sources and accelerator driven systems. They all require a MW-type proton driver system to provide sufficient flux of beams for intended research. This is a timely and well-organized workshop to formulate the strategy of CERN and European’s future development in both the facilities and science programs with potential of fundamental discoveries in the post LHC era.
The scientific community of CERN proposes a 4 MW proton driver as an anchor for its future physics program. This facility consists of a front-end system of room temperature linac of 160 MeV, and then a superconducting linac of 2.2 GeV, operating at 50 Hz, delivering 4 MW proton beam power to target. If the end use of secondary beam is of continous fashion, then there is no need of any other beam compression device. In the case of short bunch beam, a proper accumulation and bunch compression device has to be added. The following is the summary of my comments about the design and implementation of the accelerator complex (Figure 72).
The choice of the Superconducting Linac(SPL) over the Rapid-Cycle-Synchrotron (RCS) configuration is a sound choice in terms of its mature technology, reduced beam losses, and flexibility in meeting the requirements from different physics communities represented in this workshop. The choice of bulk Nb superconducting cavity construction over Copper-Nb composite can provide higher accelerating gradient to provide higher beam energy than 2.2 GeV in the fixed length of the linac, or shorter length of the linac at 2.2 GeV. It is well-known that, the bulk Nb structure is subjected to the Lorentz detuning and microphonic vibration which can cause amplitude and phase perturbation without proper compensation. Therefore, it is important to realize that there is no “show stoppers” in the proposed proton driver design, the challenge is in the careful identification and cure of emittance growth mechanism, control of beam losses, beam collimation, radiation shielding, and reliable operation.
The target/horn system is intimately coupled to the specification of the proton driver and the beam characteristics required for physics research. The beam energy, intensity, and bunch structure impact greatly on the selection of target material and its cooling requirements. The physics research requirements dictate the species of secondary beam, its flux and spectrum which couples back to the selection of target material and horn design. It is imperative that the accelerator builders, the target/horn experts and the physicists have close communications and discussions through the design and construction cycle of the facility intended. It is a common believe that the target/horn system is feasible for up to 1 MW beam power and additional R&D and prototyping is required for higher power system from 2 to 4 MW. An active R&D effort in this area is required for the decision on the required performance on the facility in few years time.
The accelerator components and operation personnel can not tolerate excessive beam losses; therefore, realistic analysis of possible beam losses, its collimations and shielding have to be carefully considered for any muti-megawatt facility. Also, considerations and provisions for reliability, availability, and maintainability have to be designed in from the very beginning. Spares, preventive maintenance and repair procedures have also to be part of the design concerns.
The accelerator facility and physics research programs conceived in this workshop can be further upgraded to higher power, or expanded into many disciplines. For the initial implementation, it is important to clearly define what is in the baseline for both the facility construction and the physics research intended to pin down the cost, schedule, and performance parameters for proper project definition. In the same vane, a well-thought out plan for its future developments in either more power, adding additional facilities, or serving different communities have to be mapped out in the beginning to minimize interference with on-going physics research and waste of components and infrastructures. With both plans in hand, a realistic staged approach can be formulated for long-term development, since both the cost and research requirements prohibit complete construction in one time.
It is apparent that it needs heavy investments in the R&D and prototyping of components to realize the plan outlined in this workshop, which no single institution can afford to complete them alone. Therefore,two conditions are necessary to fulfill this vision. The first is a firm commitment from the CERN management to a steady support of this line of R&D in both manpower and material resources. The second is the formation of an effective international collaboration in this regard. It is my own observation from my participation in the BNL VLBL neutrino proposal and muon collider collaboration in the past few years that, without active participation from CERN, the international collaboration effort will forever remain in the fragmented stage( a case in point is the MICE experiment and the 4 MW liquid mercury target development program). I strongly recommend that CERN management make its firm decision and help to create adequate support in the future R&D in the line of HPPA, as long as the short term core mission of timely completion of LHC is not compromised.
The suggested R&D items for CERN MW facility include ion source, chopper, SRF cavity and cryomodule, target and horn system should be supported with vigor both to ascertain the technical feasibility and provide sufficient base for reliable cost estimate by the LHC completion time. Early implementation of the Linac4 up to 160 MeV in 2006 can benefit both the LHC performance and the existing CERN fixed target program, CNGS and ISOLDE.
9.2 Nuclear Physics
(P. Butler, M.
Harakeh)
The NuPECC Long Range Plan 2004
(NUPECC) describes how research in all fields encompassed by nuclear science,
from the smallest scales to the largest ones, has made vigorous strides in the
last decade. Many questions have been answered. However, the answers often
raised new questions paving the way to new directions in research in our
continuing quest for the understanding of our universe from the smallest
building blocks, the leptons and quarks and the mesons that carry the forces, to
the largest structures in the cosmos. To address these questions new facilities
have been proposed or are under construction. NuPECC has recommended as the highest
priority (i) the construction of the international “Facility for Antiproton and
Ion Research (FAIR)” at the GSI Laboratory in Darmstadt and (ii) the
construction of the next-generation EURopean ISOL facility (EURISOL).
These facilities have different time-frames: the planning of FAIR will see it
completed about the same time (~ 2013) that the construction phase of EURISOL
begins.
FAIR will provide new
opportunities for research in the different subfields in nuclear science. The
envisaged facility for producing high-intensity radioactive ion beams in
In-Flight Fragmentation (IFF) is highly competitive, if not surpassing in
certain respects similar facilities either planned or under construction in the
U.S. or in Japan. With the experimental equipment available at low and high
energy and at the New Experimental Storage Ring (NESR) with its internal targets
and electron collider ring, the new facility will provide worldwide leadership
in nuclear structure and nuclear astrophysics research. This is in particular
true for research performed with short-lived exotic nuclei far from the valley
of stability. The high-energy
high-intensity stable heavy-ion beams will facilitate the exploration of
compressed baryonic matter with new penetrating probes. The high quality cooled
antiproton beams in the high-energy storage ring (HESR) in conjunction with the
planned detector system PANDA will provide the opportunity to search for new
hadron states predicted by QCD and explore the interactions of the charmed
hadrons in the nuclear medium. In short, this facility is broadly supported
since it will benefit almost all fields of nuclear science with new research
opportunities.
The Isotope Separation On-Line (ISOL) technique to produce radioactive beams has clear complementary aspects to the IFF method. First-generation ISOL-based facilities have produced their first results and have convincingly been shown to work. EURISOL aims at increasing the variety of radioactive beams and their intensities by orders of magnitude over the ones available at present for various scientific disciplines including nuclear physics, nuclear astrophysics and fundamental interactions. The presently running project is aimed at completing a design study of the EURISOL facility. Because of this time-line for EURISOL NuPECC supports projects which have intermediate planning and will be realised on a shorter time-scale. These include the second-generation ISOL facilities: SPIRAL2 (GANIL, Caen), SPES (LNL, Legnaro), the upgraded REX-ISOLDE (CERN, Geneva) and MAFF (München). The technical developments required for these intermediate-scale projects such as high-power proton/deuteron (p/d) superconducting linear accelerators (SPIRAL2, SPES), heavy-ion superconducting postaccelerator (SPIRAL2), or high-power production targets (ISOLDE) are precisely the ones needed for EURISOL. An advanced ISOL facility such as EURISOL will use a high-power (several MW) p/d accelerator. A large number of possible projects such as neutrino factory, antiproton facility, muon factory and neutron spallation source may benefit from the availability of such a p/d driver, and synergies with closely and less closely related fields of science are abundant. Considering the wide interest in such an accelerator NuPECC recommends joining efforts with other interested communities to do the RTD and design work necessary to realize the high-power p/d driver in the near future.
9.3 Particle physics
(A.
Blondel, M. Spiro)
Certainly the physics case that was presented in the workshop for a high intensity proton machine in Europe is very strong. The leading case is neutrino physics but the accompanying programs in rare muon and Kaon decays are compelling.
For neutrino physics a number of possibilities have been suggested to explore the {q13, sign(Dm213), d} paradigm. In many ways the choices or strategy should be made on the basis of the science, and probably on the basis of available funding, synergies, and timing.
The first possibility is that of two low energy beams – the superbeam and the standard beta-beam, that can aim at the same detector, a very large water Cherenkov and/or liquid argon detector situated at a short distance (O (100km)). In this first scenario there is little matter effects and the sensitivity depends on how massive the detector can be, taking account the boundary conditions due to excavation possibilities and cost, while keeping reasonable efficiency and calibration. Operating with 300-600 MeV neutrinos has the advantage of staying in the quasi-elastic region, but the cross-sections are low and poorly known with large differences between i) neutrinos and anti-neutrinos, and ii) muon neutrinos and electron neutrinos. The consequences in terms of systematics on a CP asymmetry remain to be established. On the positive side, the possibility of building both T and CP asymmetries is a remarkable feature of this combination of superbeam and beta-beam. In addition, a very large, non-magnetic detector has an excellent physics programme in its own right, being able to extend considerably the search for proton decay, astrophysical and cosmological neutrinos.
The other possibility that has been studied is the Neutrino Factory. This source of high energy (up to the muon energy, i.e. 20-50 GeV) electron neutrinos allows an even broader and more precise neutrino oscillation programme. The production of taus is allowed (silver channel) and the study of the matter resonance at 12 GeV is possible. Flux, efficiencies and backgrounds can be determined very precisely. The difficulties are twofold: first the accelerator itself is rather innovative, making it mandatory to pursue a vigorous programme of R&D to ascertain the proposed technologies (such as ionisation cooling or FFAGs) and secondly the overall cost is uncertain. The detector must be magnetic, which limits the feasibility of very large masses, and the physics programme, besides that of neutrino oscillations, of a large magnetized detector needs to be investigated. It remains without any doubt that the neutrino factory is the most powerful tool to explore CP violation, measure precisely all oscillation parameters relevant to the ‘atmospheric oscillation’ and test universality. Last but least, it is an important step towards muon colliders.
It will be important that a study of both options on equal footing of physics performance and cost be presented at the time when important decisions will need to be made, and this will require studies and R&D both on accelerator and detectors. In the framework of the ECFA/BENE study groups, the plan is to monitor these studies on a regular basis and to come up with a recommendation around 2008.
Intense beams of muons have been stressed as a powerful tool to study rare decays and leptonic flavour violation processes, which seem to be a likely outcome of many scenarios of supersymmetry. Other properties of muons (g-2, EDM) have shown to be places of choice to challenge the Standard Model. The details of targets and beam lines need to be studied, but it is clear that an accelerator like the SPL and its accumulator ring would provide great flexibility on the time structure of the beam.
Finally it is obvious that all CERN
facilities in fixed target experiments and the LHC itself can only benefit from
a source of higher brilliance and intensity.
9.4 General outlook
(Palladino for
Engelen)
9.4.1 Introduction
As discussed by J. Ellis, the physics at the High Intensity Frontier with a new MMW facility is unique and compelling. CERN appears to be a natural, if not the best, laboratory to host it.
The main focus, in the particle physics sector, is the potential offered to neutrino physics by superior neutrino beams, of conventional (superbeam) or novel (betabeam, neutrino factory) nature. Physics motivations are also very solid, in the studies of low energy muons. Mastering high brilliance muon beams holds the key to possible muon colliders.
A remarkable synergy exists with one of the most promising next generation facilities for nuclear physics and astrophysics, EURISOL; the isotope on line technique, invented in Europe in the 50’s and brought to maturity by ISOLDE at CERN, would see intensities increased by a three orders of magnitude.
The entire program appears to be compatible and synergetic with the CERN core program. It is capable to improve the performance of the LHC, the CNGS and ISOLDE, and of most existing CERN facilities.
9.4.2 Multi-Megawatt facilities in the World
The reference facility is JPARC, which is already in construction. Its initial 0.75 MW program includes the first neutrino conventional superbeam for oscillation searches over the 300 Km baseline from Tokai to Kamioka (T2K). Europe is and will be collaborating with that effort, but we must at the same time explore a possible European longer term program.
Current ideas for a possible evolution of T2K provide a natural benchmark. These include upgrade of the beam power on neutrino target to 4 MW, and a new Water Cerenkov detector of one Megaton (HyperK), similar to, but 50 times bigger than, the present one (SuperK). Following or in place of this, our Japanese colleagues pursue actively an important R&D towards a Neutrino Factory, whose present design is largely based, in the Japanese scheme, on the fixed field alternated gradient (FFAG) accelerators.
Similar MMW plans are under study also in the United States, both at BNL and Fermilab. The BNL concept features a 1.2 GeV SC linac feeding a refurbished AGS. Fermilab has two implementations under evaluation, a synchrotron and a SC linac, both at 8 Gev and capable of both stand-alone operation and of injection into the 120 GeV Main Injector.
Superior conventional neutrino beams from either laboratory could then illuminate neutrino detectors in a new Mton scale national underground science and engineering laboratory (NUSEL), in the Western part of the US, for which several locations are being proposed. The UNO collaboration, complementary and synergic with the HyperK effort, drives the effort towards design and construction of such a neutrino detector.
Beyond conventional superbeams, the US Muon Collaboration has been playing a leading role in the international effort towards a neutrino factory. By means of two full rounds of design studies, a complete preliminary design has been performed.
9.4.3 A MMW source for Europe
9.4.3.1 Proton driver
In this international context of ambitious but uncertain plans, Europe and CERN may indeed have an important role to play. Most recent studies and this Workshop have focused particularly on the possibilities that could be open by the availability at CERN of the SPL, a 4 MW few GeV/c 50 Hz superconductive proton linac, proposed as the backbone of a new European high power proton complex. Its original design was that for 3 GeV/c proton momentum but a somewhat larger momentum is possible and may be preferable in the end.
There exist other options for a MMW source of protons. Higher energy would require correspondingly fewer protons. A Rapid Cycling Synchrotron has been considered and would be perfectly suitable for Neutrino Factories. One may even consider the viability of FFAG accelerators. Further study is required to ascertain which is the best option both technically and in terms of optimal physics performance. Light should also be shed by the HARP data.
9.4.3.2 Target and collection
All these possibilities require that we learn to handle MMW proton beams. No existing target system is presently capable to sustain the thermal and mechanical stresses produced by a MMW beam. R&D is necessary to establish a convincing design providing a safe and robust solution to this problem. Most promising are liquid jet targets, although other solution are being explored too. If that problem is solved, together with the similar and related problem of designing a MMW collection systems (horn or solenoid) for secondary mesons (and muons) emerging from the target, one has created the conditions to have a MMW neutrino conventional superbeam.
9.4.3.3 Neutrino superbeam
Preliminary ideas for a neutrino superbeam have been investigated for a 3 GeV/c SPL: with a relatively short and tuneable 5-30 m pion decay tunnel downstream of the target, it would have a low average energy E, around 300 MeV. Less intense than the T2K beam, it would however be essentially free of intrinsic ne background while minimizing also inelastic neutrino interactions responsible for detector backgrounds, resulting in the end in physics performance very close to those of the T2K upgrade. Although such a superbeam could arrive only after several years of operation of T2K and may ot be defendable as a stand alone facility, it would still play an essential role in conjunction with one of the two types of novel neutrino sources, the betabeam described below.
9.4.3.4 EURISOL and the Beta-beams
A proposal of a super-ISOLDE facility, 1000 times more powerful, exists and has become known as EURISOL. Its proponents view CERN as one of the possible sites: this would enrich the panorama of CERN activities with new frontier research in nuclear physics and astrophysics, attracting a large community of new users. Remarkably, its proton driver could very well be the SPL and its high power target station(s) could closely resemble the ones being studied for neutrino applications.
The intense beams of radioactive ions produced to Eurisol, however, carry also the possibility of betabeams, novel and superior pure ne beam obtained from beta decay of the ions. Radioactive ions produced by the ISOL technique would have to be accelerated in the existing CPS and the SPS (or possibly their replacements) and then circulated in a new ion storage ring, whose straight sections would then become powerful sources of neutrinos. The most promising ions are 18Ne and 6He, producing respectively the most copious yield of ne and anti-ne. Lorentz g factors of 150 (6He) or 250 (18Ne) are possible with the SPS. The average ne energy is then very close to that of the SPL superbeam nm‘s, few hundred MeV. In order to conduct neutrino oscillation search experiments near the first maximum of oscillation probability, in the L/E variable, detector(s) of few hundred MeV neutrinos must be at a distance L, from the neutrino source at CERN, of about 100 to 150 Km. The fact that the two types of beams can use the same detector is a remarkable coincidence of great benefits.
As it requires only 5 to 10% of the SPL intensity, a Betabeam could run simultaneously with the SPL superbeam. Thanks to the very low Q value of the beta decays, these beams are much more collimated and intense, per decay, than conventional pion decay and available 18 Ne and 6He fluxes result in a comparable neutrino flux.
9.4.3.5 Megaton class detectors and experiments
Detection of those low energy, modest intensity, neutrinos from betabeams and superbeams requires new massive, low density, unprecedentedly large detectors. A Megaton Water Cerenkov detector, of the HyperK or UNO type, is again the natural default option. In Europe, however, an extra card is there to be played, the large Liquid Argon TPCs as described by Ereditato.
In the last few years it has been proposed to excavate a new large European underground laboratory in conjunction with the excavation of the new safety tunnel that will supplement the existing alpine Fréjus road tunnel. We are faced with an opportunity very similar to the one that INFN was able to exploit in the realization of the Gran Sasso Laboratory. The window of opportunity is the year 2008-2009; which sets the date for a necessary decision. While this options remains to be proved truly realistic, it has raised undoubtedly much interest and hopes and must be thoroughly explored.
The physics case for exploitation of a Megaton Water Cerenkov detector in a new Frejus laboratory in conjunction with a betabeam from CERN has been studied in detail. The discovery potential of leptonic CP violation, by means of simultaneous ne and anti-ne. running, is not very far from the one of a neutrino factory, that is still the benchmark ultimate neutrino facility for these studies. The simultaneous use of a SPL conventional superbeam, however, would open the unique opportunity to perform T and CPT violation searches. Thanks to its superior granularity, patter recognition and detection efficiency, a 0.1 Mton Li-Argon detector can be also envisaged as a detector alternative or complementary to a 5 to 10 times larger Water device.
All these considerations lead to the formulation of the first (of two) global hypothesis, ie explicit proposals for a well matched pair of neutrino source and detector site. In summary, this first possibility implies low energy, moderate flux neutrino beta-beams and superbeams pointing to a very large mass underground detector at 100 Km or so distance from CERN, in some alpine gallery. There is another remarkable synergy with the fact that this experimental approach caters also the equally compelling needs of nucleon decay studies and to those of a low energy (Supernova) neutrino observatory. The package thus offers a very attractive physics program, as was been discussed by C.K.Jung.
9.4.3.6 Neutrino Factory
The second proposal is a Neutrino Factory. This has the unique virtue of providing electron neutrinos of an energy that is high enough (up to the stored muon energy of >~20 GeV) to allow tau production as well as the crossing of the matter resonance around 12 GeV. The very high neutrino flux can be exploited with smaller -- but magnetic -- detectors, typically in the 50 Kton range. The distance from the neutrino source must be extended to match, in L/E, the multi GeV average energy E of the neutrinos. An existing underground laboratory like Gran Sasso can indeed host such a detector, but a second underground location, further away from CERN, will be needed to fully study both leptonic CP violation and the matter effects that can be used to establish the mass hierarchy of neutrinos. Candidate locations have been suggested in the extreme north of Norway and Finland as well as in a far south European location on one of the Canary islands.
The European scheme for a neutrino factory was discussed by H. Haseroth. In addition and downstream of the target and collection complex necessary for a superbeam, it includes sections devoted to the preparation of the muon beam (phase rotation, bunching and ionization cooling), to their acceleration to 20-50 GeV, and a muon storage ring of 2 km or so in circumference. The straight sections of the storage ring are sources of the neutrinos from muon decays.
The detector best suited for a Neutrino Factory is a magnetic detector sensitive to the charge of the muons. The cleanest signature of oscillation is the ne transition to a “wrong charge” nm, that has become known as the “golden channel”. The ne transition to a “wrong charge” nt , that can be studied with an ICARUS- or OPERA-like detector, has instead become known as the “silver channel” and has the merit to suppress ghost solutions in oscillation parameter space as discussed by P. Hernandez.
The physics case for this second global option, a neutrino factor serving a “modest” size magnetized detector, has been studied in detail both in the US and in Europe. It provides the strongest sensitivity to the CP violation phase and to all other relevant neutrino oscillation parameters. It emerges as the superior and ultimate line of approach to the rich phenomenology implied by our present understanding of the oscillation phenomena.
9.4.3.7 Good news
The studies that have been performed so far indicate that a Neutrino can be built now. The real challenge of the Neutrino Factory R&D is cost reduction. Good news were given by S. Geer that a revision of the cost estimates from the second US design study points to a major reduction of the cost of a Neutrino Factory down to approximately 1.3 G$, a good step closer to being ultimately affordable, and not so different from our first global option.
9.4.3.8 Near detectors and physics of neutrino interactions
On the path of neutrinos to far detectors, it will be essential to have near stations monitoring each of the two types of neutrino beams, i.e. the low energy beta-beam (and superbeam) or the high energy neutrino beam from the factory. This is the only way to keep systematic uncertainties under control. An additional reward of this near detector stations, which will enjoy fluxes several orders of magnitude higher than short baseline neutrino experiments so far, comes from the possibility of using small low mass highly sophisticated jewel detectors that will greatly enhance our knowledge of the physics of neutrino interactions.
9.4.3.9 Making choices
A choice among the two global options discussed above will probably be necessary in the not far future, in the context of consensual international coordination of regional plans and programs. The last point that deserves discussion is therefore international collaboration on the R&D efforts necessary to make one or both these options a reality somewhere in the world. A large amount of R&D is necessary in all areas: high power proton drivers, targetry and collection, muon manipulation (ionisation cooling in particular) and acceleration, neutrino detectors. All of these are in progress with a healthy level of global collaborations. Europe is likely to be able to host in the coming future several aspects of this effort. Among them, a targetry & collection demonstration experiment at the CERN PS, an international muon ionisation cooling experiment (MICE) at RAL and possibly an FFAG development and test program. This R&D effort deserves support. The rate of progress will be slow, delays should be carefully avoided for the few demonstrations that are on the critical path .
9.4.3.10 Conclusions
The European strategy in neutrino physics, adequately ambitious and aware of the international context, based on a new MMW proton driver and in synergy with nuclear physics and other sectors of particle physics, including either a beta-beam/superbeam complex and/or a Neutrino Factory complex, will receive careful attention from the CERN management and the CERN council.
10 Recommendations
10.1Recommended accelerator R&D
(R. Garoby, M. Lidroos, A. Blondel, H.
Haseroth)
10.1.1 Proton driver
For the linac proton driver solution, provided the on-going support to the development of equipment for Linac4 is steadily maintained, more efforts have to be invested in the following items, as highlighted in section 9.1 of this document:
o The H- ion source, whose characteristics are beyond today’s state-of-the-art,
o The chopper driver, for which no adequate solution has yet been found,
o The superconducting RF technology where activity has been almost stopped at CERN.
It is clear that the issue of radioprotection and the management of beam losses are crucial to the operation of a multi-MW machine, which implies strengthening efforts on beam dynamics and on the analysis of measures to limit activation (calculation of activation, selection of materials, design of collimators and beam dumps…).
For the RCS proton driver solution(s), competence and efforts are localised at RAL. For a proper comparison with the SPL option, more resources are necessary, and certainly some at CERN. Obviously, if an RCS based solution is finally selected, the resources initially invested in the SPL would be redirected.
10.1.2 Eurisol and neutrino Beta-beam
The EURISOL design study proposal concerning an ISOL and beta-beam facility, submitted to the EU sixth framework program, was favourably evaluated. Contractnegotiations between the EU and the institutes and universities participating arescheduled for September 2004. The aim is to get started in January 2004 and work for four years. The technical design work to be undertaken has been described in section 5.3. The study is presently site independent but CERN is listed as a candidate lab to host the facility considering especially the possible construction of SPL at CERN. The design study is strongly supported and the community is encouraged have a full technical design report ready for the present milestone of 2009 for a decision on SPL at CERN.
10.1.3 Superbeam and Neutrino Factory
Because of the high beam power and the resulting safety issues, the engineering design of the target and target area are crucial and challenging. For the needs of all applications, a strongly increased effort has to be invested in these fields, both for the nuclear physics applications (which are covered in the framework of EURISOL) and for the particle physics applications, which are not covered at CERN presently. The target experiment which is being proposed [target-exp] is a remarkable example of international collaboration and should be supported, but it only covers the specific aspect of the beam-target interaction in a magnetic field.
In the case of the neutrino super-beam, the design of a horn that combines neutrino flux optimisation and the capability to survive long enough the mechanical stress and the high level of radiation is a case of concern. The on-going efforts in collaboration between LAL-Orsay and CERN should be encouraged and strengthened.
The above are all necessary both for a superbeam and Neutrino Factory. The accelerator R&Ds specific of a Neutrino Factory are as follows.
n Theoretical development and optimisation of the design for cost/performance optimisation
n For the muon front-end (phase rotation and cooling): demonstration of the gradients under which RF cavities can operate in magnetic fields
n Demonstration of the practical feasibility of muon ionisation cooling (MICE experiment)
n Design and cost estimate of acceleration with FFAG
A substantial fraction of the theoretical work and the component development for the muon front end are already underway within the auspices of the Neutrino Factory and Muon Collaboration [MuColl], in particular the MUCOOL effort [Mucool].
The MICE experiment at RAL, with strong support from the UK, is an opportunity for Europe to have a major impact on this research. Support from PSI and CERN in the form of refurbished equipment is foreseen. Support and participation from other European laboratories would be highly welcome and desirable.
The R&D on FFAGs is already well underway in Japan, where the PRISM experiment is proceeding. This new technique, which could have many other applications than acceleration or phase rotation of muons, certainly deserves attention and support for the small group approaching it in Europe.
The design and R&D effort leading to a superbeam or Neutrino Factory clearly requires worldwide participation and the community involved is aiming at a world design study to be completed in 2008. This calls for determined participation from several European laboratories in a concerted way, as recommended by the European Muon Coordination Group [EMCOG]. Possibilities to obtain EU funding via a EU FP6 design study or additional JRA’s within CARE [CARE] are being investigated.
10.2Recommended detector R&D
It has been proven since the early days of neutrino detection that assembling adequately large mass detectors will not be an easy task [Strolin]. The time is ripe to face this challenge. In order for the programme to be successful our recommendations are that physicists and funding agencies in Europe
1) join the US and Japanese effort in the design of a Megaton size Water Cerenkov detector, along the lines described in section 6.3. The technique and cost of excavation of very large underground caverns has to be understood. Photosensor development and involvement of European manufacturers appears highly desirable
2) support the European R&D towards large mass Li Argon detectors. Its seed is the ICARUS Collaboration. While striving to implement the technology in its first 3 KTon application at LNGS, they are trying to design much larger devices, up to 100 Ktons, and possibly embed them in magnetic fields. Non-European participation is being actively sought.
3)launch a study of a 50 Kton large magnetic detectors (LMD) [Cervera], ideal tool for the golden channel at the neutrino factory. Options are a Super MINOS detector, 10 times larger than MINOS [MINOS] or a slightly larger implementation of the MONOLITH [MONO] design.type.
4) Given the importance of the silver channel, studies of a detectors with kink-finding capabilities, OPERA-like or otherwise, should be investigated.
10.3 Milestones
The ECFA/BENE and EURISOL communities plan to continue their joint effort, assemble the largest possible interest and constituency around a complete MMW physics program. The general “strategy” is to provide the CERN Management with
1) the appropriate documentation to support a proposal to the CERN Council at the end of 2006, consisting of a first set of limited new investments
2) a full conceptual design report for a superior MMW facility, intended to support the proposal, to the CERN Council in the course of 2009, of major new investments in the MMW sector, after LHC and before CLIC.
This schedule implies that we in Europe should continue to push vigorously the necessary R&D, solve the remaining technical challenges, make construction costs affordable and be ready with a complete technical design to start building a complex of MMW particle and nuclear physics facilities as soon as that will be possible.
A more detailed list of upcoming events is as follows:
· 2-3 November 2004, DESY: ECFA/BENE Workshop on ‘The future of accelerator based neutrino experiments in Europe' , in the framework of the general yearly CARE Meeting http://care04.desy.de/
· March 2005 (Fréjus) Megaton physics workshop
· June 2005 (Frascati) NUFACT05 : an interim set of BENE recommandations is planned
Further milestones are more tentative, but may possibly be
· End 2006 first limited new investiments at CERN (160 MeV H- linac?)
· June 2008: NUFACT08 will take place again in Europe. This is the planned time for final BENE recommendations based on comparative study of various options and will be the foreseen decision time to excavate Megaton in Fréjus.
· Around 2009 decisions on project at CERN after the LHC
References
[Adler01xv]
S. Adler et al.
, E787 Collaboration, Phys. Rev. Lett.
88 (2002) 041803 [arXiv:hep-ex/0111091].
[Ahn03]
M.H. Ahn, Phys. Rev.
Lett. 90 (2003) 041801.
[AhnK2K04]
M. H. Ahn et al. [K2K
Collaboration], arXiv:hep-ex/0402017.
[Albright00]
C. Albright et al., Physics at a
Neutrino Factory, Fermilab-FN-692, May 10, 2000, http://arXiv.org/ps/hep-ex/0008064
[Amoruso04]
S. Amoruso et al. [ICARUS
Collaboration], “Measurement of the muon decay spectrum with the ICARUS liquid
Argon TPC, The European Physical Journal C, Eur. Phys. J. C 33, 233-241
(2004).
[Amoruso04b]
S.
Amoruso et al. [ICARUS
Collaboration], “Study of electron recombination in liquid Argon with the ICARUS
TPC,” Accepted by NIM A., in press.
[Amoruso04b]
S.
Amoruso et al. [ICARUS
Collaboration], “Analysis of the liquid Argon purity in the ICARUS T600 TPC,”
NIM A516 (2004) 68-79.
[Anders89]
Anders and Grevesse, Geoch. Cosmochim. Acta 53 (1989) 197.
[Anisimovsky04hr] V. V.
Anisimovsky et al., E949 Collaboration,
[arXiv:hep-ex/0403036].
[Antonello04] M.
Antonello et al. [ICARUS Collaboration], “Detection of Cerenkov light emission
in liquid Argon,” NIM A516 (2004) 348-363.
[Apollonio02]
M. Apollonio et al., ‘Oscillation Physics with a Neutrino Factory
‘arXiv:hep-ph/0210192 in ‘ECFA/CERN Studies of a European Neutrino Factory
Complex ‘ Blondel,
A
(ed.) et al.CERN-2004-002.- ECFA-04-230,
p85
[Apollonio03]
M. Apollonio et al, Eur. Phys. J. C27 (2003) 331
K. Eguchi et al, Phys. Rev.
Lett. 90 (2003)
021802.
[Aprili02]
P. Aprili et al., ICARUS Coll., CERN-SPSC-2002-027, CERN-SPSC-P-323, Aug
2002.
[APS04] “Neutrino Factory and Beta Beam Experiments and Developments”, (Eds. S. Geer and M. Zisman), Report of the Neutrino Factory and Beta Beam Working Group, APS Multi-Divisional Study of the Physics of Neutrinos, July 2004.
[Arneodo03]
F. Arneodo et al. [ICARUS Collaboration], “Observation of long ionizing
tracks with the ICARUS T600 first half-module,” NIM A 508, 287
(2003).
[Aut01]
B. Autin et al: “A Slow-Cycling Proton Driver for a Neutrino Factory”,
Proc. 7th European Particle Accelerator Conference, EPAC’00, Vienna, June 200l;
CERN/PS 2000-015 (AE).
[Aut99]
B. Autin, A. Blondel and J. Ellis eds, CERN yellow report CERN 99-02,
ECFA 99-197
[Aysto01]
J. Aysto et al., ‘Physics with Low-Energy Muons at a Neutrino Factory
Complex’, CERN-TH/2001-231, in ‘ECFA/CERN Studies of a European Neutrino Factory
Complex ‘ Blondel,
A (ed.) et al.CERN-2004-002.- ECFA-04-230,
p259.
[Barbieri94]
R. Barbieri and L.J. Hall Phys. Lett.
B338 (1994) 212
[Barger02]
V. Barger, S. Geer, R. Raja, K. Whisnant, Phys. Rev. D63 (2001)
033002.
[Barger02a]
V. Barger, D. Marfatia and K. Whisnant, ``Breaking eight-fold
degeneracies in neutrino CP violation, mixing, and mass hierarchy,'' Phys. Rev. D65 (2002) 073023,
[arXiv:hep-ph/0112119].
[Barish74]
S. J. Barish et al., Phys. Rev. Lett. 33, 448 (1974).
[bbcern]
B. Autin et al, CERN/PS 2002-078 (OP), to be published in the proceedings
of Nufact02 (London 2002) in J. Phys. G. For more references see also
http://beta-beam.web.cern.ch/beta-beam/.
[Bellodi04]
G. Bellodi: “Electron Cloud Build-up in the ISIS Proton Synchrotron and
Related Machines”, Proceedings of the Electron Cloud Workshop ECLOUD’04, Napa,
California, April 2004.
[BENE]
Beams for European Neutrino Experiments is a Neworking Activity (http://bene.na.infn.it/) supported by the EC
and most major European Agencies in the framework of the FP6 Integrated Activity
CARE (Coordinated Accelerator R&D in Europe) http://esgard.lal.in2p3.fr/Project/Activities/Current/.
The scope of BENE is also described in more detail in the following document:
http://esgard.lal.in2p3.fr/Project/Activities/Current/Networking/N3/BENE-downsized-11.doc
[Benedikt04]
M. Benedikt, K. Cornelis,
R. Garoby, E. Metral, F. Ruggiero, M. Vretenar, “Report of the High Intensity
Protons Working Group”, CERN-AB-2004-022 OP/RF
[Bigi01]
I. I. Y. Bigi et al., ‘The Potential for Neutrino Physics at Muon
Colliders and Dedicated High Current Muon Storage Rings’ Phys. Rept. 371 (2002) 151
[arXiv:hep-ph/0106177].
[Blundell99]
S. J. Blundell, Contemp. Phys.
40, 175 (1999).
[BNL91004]
BNL910 experiment, Y. Torun, NUFACT04 Osaka, July 2004.
[Bonche85]
P.Bonche et al., Nucl.Phys.A 436 (1985) 265.
[Boone-web]
See http://www-boone.fnal.gov/cross-sections
[Bouchez03]
J. Bouchez, M. Lindroos and M. Mezzetto, arXiv:hep-ex/0310059.
[Brooks99]
M. L. Brooks et al. Phys. Rev. Lett. 83 (1999) 1521
[Bruning02]
O. Bruning et al., “LHC Luminosity and Energy Upgrade: A Feasibility
Study”, LHC Project Report 626.
[Buchalla98ba]
G.~Buchalla and A.~J.~Buras, Nucl. Phys. B548 (1999) 309
[arXiv:hep-ph/9901288].
[Burbidge57]
E.M. Burbidge et al., Rev. Mod. Phys. 29 (1957)
547.
[Burget02]
J. Burguet-Castell et al., hep-ph/0207080.
[Burguet01]
J. Burguet-Castell et al, Nucl. Phys. B608 (2001) 301
[arXiv:hep-ph/0103258].
[Burguet02]
J. Burguet-Castell et al, Nucl. Phys. B646 (2002) 301,
[arXiv:hep-ph/0207080].
[Burguet03]
J. Burguet-Castell, D. Casper, J.J. Gómez-Cadenas, P. Hernández, F.
Sanchez, hep-ph/0312068, to appear in Nucl. Phys. B.
[Cameron57]
A.G.W. Cameron, Atomic Energy of Canada, Ltd., CRL-41,
1957.
[Cappi01au]
R. Cappi et al., “Increasing the Proton Intensity of PS and SPS”
CERN-PS-2001-041-AE.
[CARE]
FP6 Integrated Activity (Coordinated Accelerator R&D in Europe) http://esgard.lal.in2p3.fr/Project/Activities/Current/.
[Casper02]
D. Casper, Nucl. Phys. Proc. Suppl. 112, 161 (2002),
hep-ph/0208030.
[CDRFair]
Conceptual Design Report “An International Accelerator Facility for Beams
of Ions
and Antiprotons”, November 2001; http://www.gsi.de/GSI;
Future/cdr
[Cervera] Invited Talk at Nufact04, the Int. Workshop on Neutrino Factories and Superbreams, Osaka, July 2004, http://www-kuno.phys.sci.osaka-u.ac.jp/~nufact04/
[Cervera00]
A. Cervera et al, Nucl. Phys. B579 (2000) 17.
[Cervera00a]
A. Cervera, F. Dydak and J.J. Gomez-Cadenas, Nucl. Instr. Meth. A 451 (2000) 123.
[Cervera04]
A. Cervera, Rencontres de Moriond, March 25th 2004.
[Chomaz99]
Ph.Chomaz and F.Gulminelli,
Phys.Lett.B447(1999)221.
[Cla02]
M.A. Clarke-Gayther: “A Fast Chopper for the ESS 2.5MeV Beam Transport
Line”, proceedings of the 8th European Particle Accelerator Conference, EPAC’02,
Paris, June 2002.
[Dauxois02]
T.Dauxois et al., ‘Dynamics and Thermodynamics of systems with long range
interactions’, Lecture Notes in
Physics vol.602, Springer (2002).
[Dececco97]
P. DeCecco at al, Nucl. Instr. And Meth. A394
(3) (1997) 287--294.
[Derrick81]
M. Derrick et al., Phys. Rev.
D23, 569 (1981).
[Dillmann04]
I. Dillmann et a., Phys. Rev. Lett., in press.
[Doke93]
T. Doke, “A Historical View On The R&D For Liquid Rare Gas
Detectors,” NIM. A 327 (1993) 113.
[Donini02]
A. Donini, D. Meloni and P. Migliozzi,
hep-ph/0206034.
[Donini02]
A. Donini, D. Meloni, P. Migliozzi, Nucl. Phys. B646 (2002) 321,
[arXiv:hep-ph/0206034]; D. Autiero
et al., ``The synergy of the golden and silver channels at the Neutrino
Factory,'' arXiv:hep-ph/0305185.
[ECFAreport] ‘ECFA/CERN studies of a European neutrino factory complex’, A. Blondel et al, ed CERN 2004-002 (2004) http://preprints.cern.ch/cernrep/2004/2004-002/2004-002.html
[Elliot02]
J.B.Elliott et al., Phys.Rev.Lett.88 (2002) 042701.
[Ellis04]
J. Ellis, “The High Intensity Frontier”, Presentation to this workshop
(to be published)
[Ereditato]
A. Ereditato and A. Rubbia, “Ideas for future liquid Argon detectors,” To
appear in Proceedings of the Third International Workshop on Neutrino-Nucleus
Interactions in the Few GeV Region, NUINT04, March 2004, Gran Sasso,
Italy.
[ESS03]
The ESS Project Volume III: Technical Report, 2002;
http://www.esseurope.de.
[euris03]
Eurisol RTD report, http://www.ganil.fr/eurisol
(2003).
[EURISOL]
http://www.ganil.fr/eurisol/
[Eurisol_web]
http://www.ganil.fr/eurisol/
[EURISOLE]
http://www.ganil.fr/eurisol/Final_Report/APPENDIX-E.pdf
[Fair]
http://www.gsi.de/zukunftsprojekt/beschleunigeranlage_e.html
[Fermi02]
Fermilab Proton Driver Study II, Fermilab-TM-2169,
2002
[Flemming04]
B. Flemming, talk given at ”Neutrino SuperBeam, Detectors and Proton
Decay”,
[Fukuda01]
S. Fukuda et al, Phys. Rev. Lett. 86 (2001) 5651.
Q.R. Ahmad et al,
Phys. Rev.
Lett. 89 (2002) 011301 and 011302.
[Fukuda98]
Y. Fukuda et al. (SuperKamiokande Collab.), Phys. Lett.
B433, 9 (1998); Phys. Lett. B436, 33 (1998); Phys. Rev. Lett. 81, 1562 (1998);
Phys. Rev. Lett. 82, 2644 (1999)
[fynbo03]
H. Fynbo et al, Nucl. Phys. A724 (2003) 493--501.
[gabrielse02]
G. Gabrielse et al, Phys. Rev. Lett. 89 (2002)
213401.
[Gallager02]
H. Gallagher, Nucl. Phys. Proc. Suppl. 112, 188
(2002).
[Garoby04]
R. Garoby, K. Hanke, A. Lombardi, C. Rossi, M. Vretenar, “Design of the
Linac4, a new Injector for the CERN Booster”, to be published in the proceedings
of the LINAC2004 conference, August 16-20, Lubeck,
Germany.
[Geer98]
S. Geer, PRD 57, 6989 (1998)
[Gerigk04]
F. Gerigk: “A New 180MeV H- Linac for Upgrades of ISIS.” Proceedings of
the 9th European Particle Accelerator Conference, EPAC’04, Lucerne, Switzerland,
July 2004.
[Gilardoni]
S. Gilardoni, PhD thesis University of Geneva (2004).
See also
Neutrino Factory notes 4, 38, 42, 77, 80, 81, 86, 126, 129, 134,138 accessible
from http://slap.web.cern.ch/slap/NuFact/NuFact/NFNotes.html
[Glendenning01]
N.K.Glendenning,
Phys.Rep.342(2001)393.
[Gomez01]
J. J. Gómez-Cadenas et al., ``Physics potential of very intense
conventional neutrino beams,'' arXiv:hep-ph/0105297.
[Greco03]
V.Greco et al., Phys.Lett.B562(2003)215.
[Gru02]
P. Gruber et al, ‘The Study of a European Neutrino Factory Complex’, Neutrino Factory Note 103(2002)
CERN/PS/2002-080(PP) , in
‘ECFA/CERN Studies of a European Neutrino Factory Complex ‘ Blondel,
A (ed.) et al.CERN-2004-002.- ECFA-04-230, p7
[gsi02]
An international accelerator facility for beams of ions and
antiprotons Conceptual Design
Report , GSI (2002).
[Guler01]
M. Guler et al., OPERA Coll., CERN-SPSC-2001-025, CERN-SPSC-M-668,
LNGS-EXP-30-2001-ADD-1, Aug 2001.
[Gulminelli03]
F.Gulminelli et al., Phys.Rev.Lett.91(2003) 202701.
[HARP03]
CERN-SPSC/2003-027, SPSC-P-325, August 2003,
[HARPlaser]
SYLP0 by Quanta Systems srl, Milano, Italy
[HARP-proposal]
The HARP experiment, proposal to
the SPSC: CERN-SPSC 99/35, SPSC P315, November 15th 1999,[K2K03] K2K
Collaboration, Phys. Rev. Lett. 90, 041801, 2003,
[Hinks48]
E.P. Hinks and B. Pontecorvo, Phys. Rev. Lett. 73 (1948)
246
[Hip_web]
http://ab-div.web.cern.ch/ab-div/Projects/hip/
[Hippi_web]
http://mgt-hippi.web.cern.ch/mgt-hippi/
[Hisano99]
J. Hisano and N. Nomura, Phys. Rev. D59 (1999)
116005
[huang03]
W. Huang et al, Europhys. Lett. 63 (2003) 687--693.
[Huber02]
P. Huber, M. Lindner and W. Winter, Nucl. Phys. B645 (2002) 3,
[arXiv:hep-ph/0204352].
[Huber03]
P. Huber and W. Winter; Phys. Rev. D68, 037301(2003); hep/ph-0301257.
[Itow01]
Y. Itow et al., Nucl.
Phys.
Proc. Suppl. 111 (2002) 146.
arXiv:hep-ex/0106019.
[Japnufact]
A Feasibility Study of A Neutrino
Factory in Japan, Y. Kuno, ed.,
http://www-prism.kek.jp/nufactj/index.html
[Jnufact]
http://www-ps.kek.jp/jhf-np/LOIlist/pdf/L27.pdf and references
therein
[jparc]
http://j-parc.jp/ and references therein
[JPARC]
Japan Proton Accelerator Research Complex J-PARC http://jkj.tokai.jaeri.go.jp/
[Jparc_web]
http://j-parc.jp/
[jparclois]
http://www-ps.kek.jp/jhf-np/LOIlist/LOIlist.html
[Jungmann]
K. Jungmann, private communication
[KamLAND02] K. Eguchi et al.,
KamLAND Coll., First Results from KamLAND: Evidence for Reactor Anti-Neutrino
Disappearance, Phys. Rev.
Lett. 90 (2003) 021802 -- hep-ex/0212021.
[KamLAND04]
KamLAND
collaboration, Measurement of neutrino oscillations with KamLAND: Evidence of
spectral distortion, hep-ex/040621.
[Kappeler98]
F. Käppeler et al., Ann. Rev. Nucl. Part. Sci. 48 (1998)
175.
[Keil00]
E. Keil, A 50 GeV Muon Storage Ring Design, NUFACT note 26 http://slap.web.cern.ch/slap/NuFact/NuFact/nf26.pdf
see also NUFACT notes 32, 33 and 48.
[Keil04]
E. Keil and A. Sessler, Nufact note 132, http://slap.web.cern.ch/slap/NuFact/NuFact/nf132.pdf
[Kitao02]
R. Kitano et al., Phys. Rev.
D66 (2002) 096002, M. Koike, Theoretical study on the Lepton Flavour Violating µ
- e conversion in nuclei, proc NUFACT03.
[Kratz00]
K.-L. Kratz et al., in “Origin of Elements in the Solar System:
Implications of Post-1957 Observations”, ed. O.
Manuel (Kluver Academic/Plenum, 2000) p. 119.
[Krenz78]
W. Krenz et al., Nucl. Phys.
B135, 45 (1978).
[Kubik02]
D. Kubik et al., to be submitted to Nucl. Instrum.
Meth.
[Lang01]
K. Lang et al., MINOS Coll., Nucl. Instrum.
Meth. A461, 290 (2001).
[Lasserre02]
T. Lasserre et al, LENS Coll., Prog. Part.
Nucl. Phys. 48, 231 (2002).
[Lattimer77]
J.M. Lattimer et al., Ap. J. 213 (1977) 225.
[Lee77]
W. Lee et al., Phys. Rev. Lett. 38, 202 (1977).
[leptogenesis]
M. Fukugita and T. Yanagida, Phys. Lett. 174B (1986)
45.
[Lindner02]
M. Lindner, The physics potential of future long baseline neutrino
oscillation experiments, to appear in Neutrino Mass, Springer Tracts in Modern
Physics, ed. G. Altarelli and K. Winter, hep-ph/0209083
(2002)
[Lindroos03]
M. Lindroos, talk at the Moriond Workshop on ``Radioactive beams for
nuclear physics and neutrino physics'',
http://moriond.in2p3.fr/radio/.
[lindroos04]
M. Lindroos, private communivation
[Lodders03]
K. Lodders, Ap. J. 591 (2003) 1220.
[Lombardi]
A. Lombardi, ‘A 40-80 MHz System for Phase Rotation and Cooling’, Nufact
Note 34. See also notes 41, 102, 119.
http://slap.web.cern.ch/slap/NuFact/NuFact/NFNotes.html
[Lrplan04]
“The Coming Revolution in Particle Physics--Report of the Fermilab Long
Range Planning Committee”, Fermilab-TM-2253, 2004, http://www.fnal.gov/directorate/Longrange/Long_range_planning.html
[Mangano01]
M. L. Mangano et al., ‘Physics at the front-end of a neutrino factory: a
quantitative appraisal’ arXiv:hep-ph/0105155, in ‘ECFA/CERN Studies of a
European Neutrino Factory Complex ‘ Blondel,
A (ed.) et al.CERN-2004-002.- ECFA-04-230, p187
[McGrew04]
C. McGrew, talk given at ”Neutrino SuperBeam, Detectors and Proton
Decay”,
[MEG]
The MEG experiment: search for the m®eg
at PSI, September 2002, available at http://meg.psi.ch/docs/prop_infn/nproposal.pdf
[Mezzetto03]
M. Mezzetto, J. Phys. G.29 (2003) 1771 and 1781.
[MICE]
The International Muon Ionization Experiment MICE,
http://hep04.phys.iit.edu/cooldemo
[Minakata01]
H. Minakata and H. Nunokawa, JHEP 0110 (2001) 1,
[arXiv:hep-ph/0108085].
[MiniBoone]
MiniBooNE Collaboration, http://www-boone.fnal.gov,
[Minos]
http://www-numi.fnal.gov:8875/public/index.html
[MIPP]
The MIPP experiment web site http://ppd.fnal.gov/experiments/e907/e907.htm
[Monolith]
‘Monolith, a massive
magnetized iron detector for neutrino oscillation studies’ LNGS-P26-2000, LNGS-P26-00,
CERN-SPSC-2000-031, CERN-SPSC-M-657, Aug 15th, 2000.
[MuColl]
The Muon Collider and Neutrino Factory Collaboration, see the web site http://www.cap.bnl.gov/mumu/ which
contains also references to several physics studies.
[Mucool]
The Muon Cooling Experimental R&D http://www.fnal.gov/projects/muon_collider/cool/cool.html
[Mueller95]
H.Mueller, B.D.Serot, Phys.Rev.C 52 (1995) 2072.
[muoncollider]
See for instance S. Kramlet al, ,Physics opportunities at m+m- Higgs
factories, in [ECFAreport], p 337.
[Muons_web]
http://muonstoragerings.web.cern.ch/muonstoragerings/
[Murayama02] H.
Murayama, Int. J. Mod. Phys. A17, 3403 (2002).
[NA48EOI04]
CERN-SPSC-2004-010
SPSC-EOI-002 http://na48.web.cern.ch/NA48/NA48-3/index.html
[NA49]
NA49 Collaboration, Nucl. Instrum. Meth.
A430 (1999) 210; Nucl. Instrum. Meth. A451 (2000) 406; NA52 Collaboration, Nucl.
Phys. A 590 (1995) 347C; PAMELA Collaboration, 27th International Cosmic Rays
Conference, OG
[Natowitz02]
J.B.Natowitz et al., Phys.Rev. C65 (2002) 034618.
[neutrinofits]
see for instance M.C.
Gonzalez-Garcia, Michele
Maltoni, hep-ph/0406056,
John N.
Bahcall, M.C.
Gonzalez-Garcia, Carlos
Pena-Garay , hep-ph/0406294;
G.L.
Fogli et al hep-ph/0310012
[Nienaber]
P. Nienaber, Ph. D. thesis, Univerity of Illinois at Urbana-Champaign
(1988).
[nufact]
S. Geer, Phys. Rev. D57 (1998) 6989; A. De Rújula, M.B. Gavela and P. Hernández, Nucl. Phys. B547 (1999) 21; A. Blondel et al., Nucl.
Instrum. Methods Phys. Res., A 451 (2000) 102; For recent reviews see M. Apollonio, et al, in
CERN-04/02, (2004)
arXiv:hep-ex/0210192; J. J. Gómez-Cadenas and D.A. Harris, ``Physics
opportunities at neutrino factories,''
Ann. Rev. Nucl. Part. Sci. 52} (2002) 253 and the annual proceedings of the
International Nufact Workshop.
[NuFactPhys]
S. Geer, PRD 57, 6989 (1998); B. Autin, A. Blondel and J. Ellis eds, CERN
yellow report CERN 99-02, ECFA 99-197; C. M. Ankenbrandt et al., Phys. Rev. ST
Accel. Beams
2, 081001 (1999); A. Blondel et al., Nucl. Instrum. Methods Phys. Res., A 451
(2000) 102; C. Albright et al., FERMILAB-FN-692, hep-ex/0008064; D. Harris et
al., Snowmass 2001 Summary, hep-ph/0111030; A. Cervera et al., Nucl.
Phys.
B579, 17 (2000), Erratum-ibid.B593:731-732,2001; M. Koike and J. Sato, Phys.
Rev. D62 (2000) 073006.
[NUMI]
A. Para and M. Szleper,``Neutrino oscillations experiments using off-axis
NuMI beam,'' arXiv:hep-ex/0110032; D. Ayres {\it et al}, arXiv:hep-ex/0210005.
[NUMIOffAxis] http://www-off-axis.fnal.gov/loi.ps,
Letter of intent to build an off-axis detector to study
oscillations
with the NuMI neutrino beam, August 2002.
[nupec03]
Nupecc long range plan, http://www.nupecc.org
(2003).
[NUPECCLRP] http://www.nupecc.org/lrp02/long_range_plan_2004.pdf
[PDG02]
K. Hagiwara et al., Review of Particle Properties, Phys. Rev. D66, 010001
(2002), also available at http://pdg.lbl.gov
[PDWG01]
Report of M4 Proton Driver Working Group, Snowmass, July 2001.
[Pfeiffer01]
B. Pfeiffer et al., Nucl. Phys. A693 (2001) 282.
[Pfeiffer96]
B. Pfeiffer et al., Acta Physica Polonica B27 (1996)
475.
[Pilaftsis99]
A. Pilaftsis, Int. J. Mod. Phys. A14, (1999)
[PMNS]
B. Pontecorvo, Sov. Phys. JETP 6 (1957) 429 [Zh. Eksp. Teor. Fiz. 33
(1957) 549]; Z. Maki, M. Nakagawa and S. Sakata, Prog. Theor. Phys. 28 (1962) 870;
B. Pontecorvo, Sov. Phys. JETP 26 (1968) 984 [Zh. Eksp. Teor. Fiz. 53 (1967)
1717]; V. N. Gribov and B. Pontecorvo, Phys. Lett. B 28 (1969)
493.
[Prior00]
C.R. Prior and G.H. Rees: “RAL Proton Driver Studies for a Neutrino
Factory”, Proceedings of the Neutrino Factory Workshop, NUFACT’00, Monterey,
California, June 2000.
[Prior00a]
C.R. Prior and G.H. Rees: “Synchrotron-based Proton Drivers for a
Neutrino Factory”, Proceedings 7th
European Particle Accelerator Conference, EPAC’00, Vienna, June
2000.
[Prior03b]
C.R. Prior: “Space Charge Simulation”, Proceedings of 29th ICFA Advanced
Beam Dynamics Workshop on Beam Halo Dynamics, Diagnostics and Collimation,
Montauk, NY, May 2003.
[Prior93]
C.R. Prior: “Study of Dual Harmonic Acceleration in ISIS”, Proceedings of
XIIth International Collaboration on Advanced Neutron Sources, ICANS-XII,
Abingdon, UK, May 1993.
[Prior99]
C.R. Prior: “Funnel Studies for the European Spallation Source”, ESS
Report ESS-99-96A, ISSN 1443-559X.
[Rigolin04]
S. Rigolin, ‘Why care about (q13, d) degeneracy at future neutrino
experiments’, Rencontres de Moriond 2004, to appear in the proceedings (2004),
arXiv:hep-ph/0407009
[Rosswog00]
S.K. Rosswog et al., A&A 360 (2000) 171.
[Rubbia04] A.Rubbia, “Experiments for CP-violation: a giant liquid argon scintillation, Cerenkov and charge imaging experiment”, arXiv:hep-ph/0402110.
[Rubbia77]
C. Rubbia, “The Liquid Argon Time projection Chamber: a new concept for
Neutrino Detector”, CERN–EP/77–08, (1977).
[Ruj99]
A. De Rujula, M.B. Gavela, P. Hernandez, Nucl. Phys. B547 (1999) 21,
arXiv: hep-ph/9811390.
[Sanders]
D. Sanders et al., IEEE Trans. Nucl. Sci. 49 (2002)
1834.
[Schatz01]
H. Schatz et al., Phys. Rev. Lett. (2001) 3471.
[Schatz98]
H. Schatz et al., Physics Reports 294 (1998) 167.
[Schrenberg01]
R.P.Schrenberg et al., Phys.Rev.C 64 (2001)
054602
[seesaw]
M. Gell-Mann, P. Ramond and R. Slansky, in Supergravity, edited by P. van
Nieuwenhuizen and D. Freedman, (North-Holland, 1979), p. 315; T. Yanagida, in
Proceedings of the Workshop on the Unified Theory and the Baryon Number in the
Universe, edited by O. Sawada and A. Sugamoto (KEK Report No. 79-18, Tsukuba,
1979), p. 95; R.N. Mohapatra and G. Senjanovi´c, Phys. Rev.Lett. 44 (1980)
912.
[SNO01]
Q. R. Ahmad et al., SNO Coll, Phys. Rev. Lett. 87, 071301
(2001)
[SNO02]
Q. R. Ahmad et al., SNO Coll., nucl-ex/0204008.
[Spl_web]
http://ps-div.web.cern.ch/ps-div/SPL_SG/
[splcern]
B. Autin et al, CERN/PS
2002-012.
[STORI02]
Proceedings of the “5th International Conference on Nuclear Physics at
Storage Rings” (STORI02),
Uppsala, Sweden, June 16 - 20, 2002, eds. H. Calén and C. Ekström, Physica Scripta T104
(2003)
[strasser04]
P. Strasser et al, in press.
[strasser99]
P. Strasser et al, Hyperfine Interactions 119 (1999) 317.
[Strolin] Invited Talk at Nufact04, the Int. Workshop on Neutrino Factories and Superbreams, Osaka, July 2004, http://www-kuno.phys.sci.osaka-u.ac.jp/~nufact04/
[StudyI]
Feasibility Study on a Neutrino Source Based on a Muon Storage Ring,
D.Finley, N.Holtkamp, eds. (2000), http://www.fnal.gov/projects/muon_collider/reports.html
[StudyII]
‘Feasibility Study-II of a Muon-Based Neutrino Source’, S. Ozaki, R.
Palmer, M. Zisman, and J. Gallardo, eds. BNL-52623, June 2001, available at http://www.cap.bnl.gov/mumu/studyii/FS2-report.html
; M.M. Alsharo’a et al., Phys. Rev. ST Accel. Bemas 6, 081001
(2003).
[Suess56] H.E. Suess and H.C. Urey, Rev. Mod. Phys. 28 (1956) 53.
[T2K]
http://neutrino.kek.jp/jhfnu/ and references
therein
[target-exp]
.R.J. Bennett et al, ‘Studies of a target system for a 4MW 24 GeV proton
beam’, CERN-INTC proposal 2003-033, April 2004.
[Tesla01]
TESLA Technical Design Report, March 2001
[Tsang04]
M.B.Tsang et al., Phys.Rev.Lett.92 (2004) 062701.
[turrion03]
M. Turrión, O. Tengblad, Targisol web database, http://www.targisol.csic.es/ (2003).
[UNO]
M. Goodman, et al, ``Physics
Potential and feasibility of UNO'', ed. D. Casper, C.K. Jung, C. McGrew and C.
Yanagisawa, SBHEP01-3 (July 2001).
[Vretenar00]
M. Vretenar (editor), “Conceptual Design of the SPL, A High Power
Superconducting H- Linac at CERN”, CERN 2000-012.
[Welford]
W. T. Welford, R. Winston, The optics of non-imaging concentrators,
Academic Press, New York, 1978, H. Hinterberger, R. Winston, Rev. Sci. Instr. 37
(1966) 1094
[Weng03]
W.T. Weng et al, “The Neutrino Superbeam from the AGS”, Journal of
Physics G, 29, (2003) 1735
[Wiescher98]
M. Wiescher, in Nuclear and Particle Astrophysics, eds. J.G. Hirsch and
D. Page. (1998) p. 79.
[Willis94]
W. J. Willis and V. Radeka, “Liquid Argon Ionization Chambers As Total
Absorption Detectors,” NIM 120, 221 (1974).
[Woosley94]
S. E. Woosley et al., Ap. J. 433 (1994) 229.
[Zeller03]
G. P. Zeller, arXiv:hep-ex/0312061.
[Zucchelli]
P. Zucchelli, Phys. Lett. B532 (2002) 166.
Workshop Organization, Participants and
Programme
Local Organizing
Committee:
M. Benedikt (CERN), A. Blondel (Geneva),
P.Butler (co-chair), L. Ghilardi (CERN), G. Giudice (CERN), E. Gschwendtner
(Geneva), M. Lindroos, V. Palladino (co-chair), M. Vretenar
(CERN)
Programme Committee:
A. Blondel
(Geneva) , A. Baldini (Pisa), Y. Blumenfeld (IPN Orsay), P. Butler (CERN),
P. Debu (Saclay), R. Edgecock (RAL), J. Ellis (CERN), R. Garoby (CERN), U.
Gastaldi (Legnaro), M. Lindroos (CERN), V. Palladino (Napoli), J. Panman (CERN),
C. Prior (RAL), A. Rubbia (ETH Zurich), P. Schmelzbach (PSI)
Scientific Advisory Committee:
J.
Äystö (Jyväskylä), R. Aleksan (Saclay), M. Baldo Ceolin (Padova), J. Bouchez
(Saclay),
E. Coccia (G. Sasso), J. Dainton (Liverpool), J.-P. Delahaye
(CERN), C. Detraz (CERN), R. Eichler (PSI), J. Engelen (CERN), Feltesse (Saclay), E. Fernandez
(Barcelona),
G. Fortuna (Legnaro), B. Foster (Oxford), W. Gelletly (Surrey),
D. Goutte (GANIL), D. Guerreau (IN2P3), M. Harakeh (KVI Groningen), H. Haseroth
(CERN). W. Henning (GSI), E. Iarocci (INFN), B. Jonson (Göteborg), K. Jungmann
(KVI Groningen), B. Kayser (Fermilab), M. Lindner (TU Munich), L. Mosca
(Saclay), A. Müller (IPN Orsay), S. Nagamiya (JPARC), M. Napolitano (Napoli), W.
Nazarewicz (Oak Ridge), K. Peach (RAL), R. Petronzio (Roma II), F. Ronga
(Frascati), D. Schlatter (CERN), M. Spiro (IN2P3),
I. Tanihata (RIKEN), C.
Wyss (CERN), J. Zinn-Justin (DAPNIA)
Table 16 List of participants:
|
ADELMANN |
ANDREAS |
Paul
Scherrer Institut (PSI) |
Villigen |
Switzerland |
|
ALEKSAN |
ROY |
CPPMarseille |
Marseille |
France |
|
AMSLER |
CLAUDE |
Physik-Institut
der Universität Zürich |
Geneva |
Switzerland |
|
ANGHINOLFI |
MARCO |
INFN |
Genova |
Italy |
|
APOLLONIO |
MARCO |
University
of Trieste and INFN |
Trieste |
Italy |
|
ASLANIDES |
ELIE |
CPPMarseille |
Marseille |
France |
|
AYSTO |
JUHA |
Department
of Physics |
Jyvaskyla |
Finland |
|
BALDINI |
ALESSANDRO |
INFN
- Pisa |
Pisa |
Italy |
|
BALDO
CEOLIN |
MILLA |
University
of Padova, Physics Dept. |
Padova |
Italy |
|
BENNETT |
ROGER |
CCLRC |
Didcot |
UK |
|
BLONDEL |
ALAIN |
DPNC |
Geneve |
Switzerland |
|
BLUMENFELD |
YORICK |
Institut
de Physique Nucleaire |
Orsay |
france |
|
BONESINI |
MAURIZIO |
INFN
- Milano |
Milano |
Italy |
|
BOOTH |
CHRIS |
University
of Sheffield |
Sheffield |
UK |
|
BOUCHEZ |
JACQUES |
CEA/DAPNIA |
Gif-sur-Yvette |
France |
|
BUTLER |
PETER |
CERN |
Geneva |
Switzerland |
|
CALABRETTA |
LUCIANO |
INFN-LNS |
Catania |
ITALY |
|
CAMPAGNE |
JEAN-ERIC |
LAL |
Orsay |
France |
|
CATANESI |
MARIA-GABRIELLA |
INFN
Bari |
Bari |
Italy |
|
CAVATA |
CHRISTIAN |
CEA
Saclay |
Gif/Yvette |
France |
|
CAZES |
ANTOIEN |
Laboratoire
de L'accélérateur Linéaire |
Orsay |
France |
|
CECCUCCI |
AUGUSTO |
CERN |
Geneva |
Switzerland |
|
CERVELLI |
FRANCO |
INFN
pisa |
pisa |
Italy |
|
CERVERA |
ANSELMO |
DPNC
Uni Geneva |
Geneva |
Switzerland |
|
CHIHIRO |
OHMORI |
KEK |
Tsukuba |
Japan |
|
CHMIELEWSKA |
DANKA |
Institute
for Nuclear Studies (IPJ) |
Warsaw |
POLAND |
|
CIAVOLA |
GIOVANNI |
INFN-LNS |
Catania |
Italy |
|
CORNELL |
JOHN |
GANIL |
CAEN |
France |
|
DE
BELLEFON |
ALAIN |
PCC-Collège
de France |
Paris |
France |
|
DEBU |
PASCAL |
CEA
/ Saclay |
Gif/Yvette |
France |
|
DECLAIS |
YVES |
IPNL |
Villeurbanne |
France |
|
DECONTO |
JEAN-MARIE |
LPSC
CNRS/IN2P3 |
Grenoble |
France |
|
DENDOOVEN |
PETER |
KVI |
Groningen |
Netherlands |
|
D'HOSE |
NICOLE |
DAPNIA/SPhN |
CEA-
Saclay |
France |
|
DORNAN |
PETER |
Imperial
College |
London |
UK |
|
DORSIVAL |
ALEXANDRE |
CERN-SC-RP |
Geneva |
Switzerland |
|
DOSSELLI |
UMBERTO |
I.N.F.N.
Padova |
Padova |
Italy |
|
DUCHESNEAU |
DOMINIQUE |
LAPP,
Annecy |
Annecy-le-Vieux |
France |
|
ENQVIST |
TIMO |
CUPP
- Pyhäsalmi |
Pyhäsalmi |
Finland |
|
EREDITATO |
ANTONIO |
INFN
Napoli |
Napoli |
Italy |
|
FACCO |
ALBERTO |
INFN-LNL |
Padova |
Italy |
|
FAVIER |
JEAN |
LAPP |
Annecy |
France |
|
FELTESSE |
JOEL |
CEA/DSM/DAPNIA-Saclay |
Gif-sur-Yvette |
France |
|
FINDLAY |
DAVID |
RAL-
CCLRC |
Didcot |
United
Kingdon |
|
FORTUNA |
GRAZIANO |
INFN
Laboratori Nazionali di Legnaro |
Legnaro
(PD) |
ITALY |
|
FRAILE |
LUIS
MARIO |
CERN |
Geneva |
Switzerland |
|
FYNBO |
HANS
O. U. |
Department
of Physics, Univ. Aarhus |
Aarhus
C |
Denmark |
|
GAROBY |
ROLAND |
CERN |
Geneva |
Switzerland |
|
GASTALDI |
UGO |
INFN-LNL Legnaro |
Legnaro
(Pd) |
Italy |
|
GEER |
STEVE |
FNAL |
Batavia |
USA |
|
GELLETLY |
WILLIAM |
The
University of Surrey |
Surrey |
UK |
|
GERBIER |
GILLES |
CEA
Saclay -DAPNIA/SPP |
Gif
s Yvette |
France |
|
GILARDONI |
SIMONE |
DPNC
Uni Geneva |
Geneva |
Switzerland |
|
GRÉGOIRE |
GHISLAIN |
University
of Louvain |
Louvain-la-Neuve |
Belgium |
|
GRIECO |
GIOVANNI |
CAEN
SpA |
Viareggio |
Italy |
|
GSCHWENDTNER |
EDDA |
DPNC
Uni Geneva |
Geneva |
Switzerland |
|
GULMINELLI |
FRANCESCA |
Laboratoire
de Physique Corpusculaire |
Caen |
France |
|
HABS |
DIETRICH |
LMU
München |
Munich |
Germany |
|
HANCOCK |
STEVEN |
CERN |
Geneva |
Switzerland |
|
HANKE |
KLAUS |
CERN |
Geneva |
Switzerland |
|
HARAKEH |
MUHSIN |
Kernfysisch
Versneller Instituut |
Groningen |
the
Netherlands |
|
HASEROTH |
HELMUT |
CERN |
Geneve |
Switzerland |
|
HERNANDEZ |
PILAR |
University
of Valencia |
Valencia |
Spain |
|
HILSCHER |
DIETRICH |
Hahn-Meitner-Institute |
Berlin |
Germany |
|
HOLMES |
STEPHEN |
Fermilab |
Batavia,
IL |
USA |
|
HUYSE |
MARK |
Instituut
voor Kern- en Stralingsfysica |
Leuven |
Belgium |
|
JEPPESEN |
HENRIK |
Department
of Physics and Astronomy |
Aarhus |
Denmark |
|
JOKINEN |
ARI |
Department
of Physics |
Jyvaskyla |
Finland |
|
JONSON |
BJÖRN |
Experimental
Physics |
Göteborg |
Sweden |
|
JUNG |
CHANG
KEE |
Stony
Brook University |
Stony
Brook, NY |
USA |
|
JUNGMANN |
KLAUS |
Kernfysisch
Versneller Instituut |
Groningen |
Netherlands |
|
KALANTAR |
NASSER |
Kernfysisch
Versneller Instituut |
Groningen |
Netherlands |
|
KATSANEVAS |
STAVROS |
IN2P3 |
Paris |
France |
|
KAYIS
TOPAKSU |
AYSEL |
CERN
and Uni. Cukurova, Adana |
Geneva |
Switzerland |
|
KESTER |
OLIVER |
MPU
München |
Munich |
Germany |
|
KIRK |
HAROLD |
BNL |
NY |
USA |
|
KLUGE |
H.-JÜRGEN |
GSI |
Darmstadt |
Germany |
|
KOJIMA |
YASUAKI |
Grad.
School of
Eng., Hiroshima University |
Hiroshima |
Japan |
|
KÖRNER |
GABRIELE-ELISABETH |
NuPECC |
Garching |
Germany |
|
KRATZ |
KARL |
Institut
für Kernchemie Universität Mainz |
Mainz |
Germany |
|
KUGLER |
ANDREJ |
Nuclear
Physics Institute ASCR |
Rez |
Czech
Republic |
|
KURCEWICZ |
WIKTOR |
Inst.
Exp. Physics,
Warsaw University |
Warsaw |
Poland |
|
LAVAGNO |
ANDREA |
Politecnico
- Dipartimento di Fisica |
Torino |
Italy |
|
LETTRY |
JACQUES |
CERN-AB |
Geneva |
Switzerland |
|
LINDNER |
MANFRED |
Technical
University Munich |
Garching |
Germany |
|
LINDROOS |
MATS |
CERN |
Geneva |
Switzerland |
|
MAMATOV |
YASHAR |
Samarkand
|
Samarkand |
Uzbekistan |
|
MASULLO |
MARIA
ROSRIA |
Istituto
Nazionale di Fisica Nucleare |
Napoli |
Italy |
|
MÉOT |
FRANÇOIS |
CEA
DAPNIA |
Gif
sur Yvette |
France |
|
MEZZETTO |
MAURO |
INFN |
Padova |
Italy |
|
MIGLIOZZI |
PASQUALE |
INFN
Napoli |
Napoli |
Italy |
|
MORI |
YOSHIHARU |
KEK |
Tsukuba |
Japan |
|
MOSCA |
LUIGI |
CEA-Saclay |
Gif-sur-Yvette |
France |
|
MOSNIER |
ALBAN |
CEA/Saclay |
Gif-sur-Yvette |
FRANCE |
|
MUCIACCIA |
MARIATERESA |
University
& INFN, BARI |
Bari |
Italy |
|
MUELLER |
ALEX C. |
CNRS-IN2P3 |
Orsay |
France |
|
MULLER |
ANDRÉ |
CERN |
Geneva |
Suisse |
|
MUSSA |
ROBERTO |
INFN
Torino |
Torino |
Italy |
|
NAGAMIYA |
SHOJI |
KEK |
Tsukuba-shi |
Japan |
|
NAKAMURA |
KENZO |
KEK |
Tsukuba |
Japan |
|
NAPOLITANO |
MARCO |
University
"Federico II" and INFN |
Napoli |
Italy |
|
NGUYEN |
HOGAN |
Fermilab |
Batavia |
USA |
|
NILSSON |
THOMAS |
Inst.
of Nuclear Physics, TU Darmstadt |
Darmstadt |
Germany |
|
OTTO |
THOMAS |
SC-RP,
CERN |
Geneve |
Switzerland |
|
PALLADINO |
VITTORIO |
University
Napoli |
|
Italy |
|
PANMAN |
JAAP |
CERN |
Geneve
23 |
Switzerland |
|
PAOLUZZI |
MAURO |
CERN |
Meyrin |
Switzerland |
|
PEACH |
KEN |
RAL |
Didcot |
UK |
|
PIERRE |
FRANÇOIS |
CEA
Saclay |
Gif/Yvette |
France |
|
REPELLIN |
JEAN-PAUL |
Laboratoire
de l'Accélérateur Linéaire |
Orsay |
France |
|
RIISAGER |
KARSTEN |
Department
of Physics and Astronomy |
Aarhus
C |
Denmark |
|
ROSSI |
CARLO |
CERN |
Geneva |
Switzerland |
|
RUBBIA |
ANDRÉ |
Institute
for Particel Physics of ETHZ |
Zurich |
Switzerland |
|
RUBBIA |
CARLO |
ENEA-Univ.
Pavia |
Geneva |
Switzerland |
|
SANDSTRÖM |
RIKARD |
DPNC
Uni Geneva |
Geneva |
Switzerland |
|
SCHLATTER |
DIETER |
CERN |
Geneva |
Switzerland |
|
SCHMELZBACH |
PIERRE |
Paul
Scherrer Institute |
Villigen
PSI |
Switzerland |
|
SCHROEDER |
W.
UDO |
University
of Rochester |
Rochester |
USA |
|
SPIRO |
MICHEL |
IN2P3 |
Paris |
France |
|
STROLIN |
PAOLO |
University
and INFN, Naples |
Napoli |
Italy |
|
SUJKOWSKI |
ZIEMOWID |
Institute
for Nuclear Studies |
Warsaw |
Poland |
|
TENGBLAD |
OLOF |
IEM-CSIC |
Madrid |
Spain |
|
TERRANOVA |
FRANCESCO |
INFN-Frascati |
Frascati |
Italy |
|
TERRIEN |
YVES |
Commissariat
à l'Energie Atomique |
Gif
sur Yvette |
France |
|
TORTORA |
LUDOVICO |
INFN - Roma III |
Rome |
Italy |
|
TRONCI |
CESARE |
University
of Torino |
Torino |
Italy |
|
TUOMINIEMI |
JORMA |
Institute
of Physics |
Helsinki |
Finland |
|
VAN
DUPPEN |
PIET |
K.U.Leuven,
University of Leuven |
Leuven |
Belgium |
|
VOLPE |
MARIA
CRISTINA |
Institut
de Physique Nucléaire Orsay |
Orsay |
France |
|
VRETENAR |
MAURIZIO |
CERN |
Geneva |
Switzerland |
|
WARK |
DAVID |
Imperial
College London |
London |
UK |
|
WARNER |
DAVID |
CCLRC
Daresbury Laboratory |
Warrington |
UK |
|
WENG |
B.
WU-TSUNG |
Brookhaven
National Laboratory |
Upton |
USA |
|
WOODS |
PHILIP |
University
of Edinburgh |
Edinburgh |
UK |
