The CERN and ECFA studies of a EUROPEAN NEUTRINO FACTORY COMPLEX
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A neutrino factory based on a muon storage ring is the ultimate tool for studies of neutrino oscillations, including possibly leptonic CP violation. It is also the first step towards muon colliders. Physics with the high intensity proton driver is already quite attractive. The aim of the studies as defined by the muon steering group (MUG) in agreement with the CERN management  is to have a Conceptual Design Report for a European Neutrino Factory Complex ready by  about 2006, i.e. the first LHC collisions. This date is chosen to allow sufficient time for the international decision process that should lead to the beginning of construction as soon as LHC financement is completed, around 2010. In this way, by 2007, CERN would have two valid options for the future: CLIC and a Neutrino Factory Complex. A choice between these two options will depend on physics and on the development of other projects such as the next linear collider, neither of which is known today.

A first round of studies has shown that a neutrino factory could probably be built with accessible technologies, and with performances matching the requirements of an exciting physics programme. The cost evaluations are however quite high (US$ 1.9 Billion from the US study)  and the techniques envisaged have often never been applied in practice. Many appealing and partially explored options exist for several of the subsystems. It thus appears that a sizeable programme of R&D will be necessary.

This note is organised as follows. The present organizational structure is described first, followed by a review of the activities of the working groups. Finally, the projects under preparation and for which support will be required are described.

 organization

 present organisation
 Towards the creation of a European collaboration for accelerator R&D
 Working groups activities
 accelerator
 ECFA physics working groups
 R&D experiments
 Projects in preparation
 International Muon ionization cooling experiment
 Large Magnetic Detector
 Low energy neutrino superbeam
 conclusions

 Appendix 1. Ongoing collaborations
 Appendix 2  Collaboration structure of the muon international cooling experiment

ORGANIZATIONAL STRUCTURE:

Present organisation:

Muon Steering group (MUG):
Alain Blondel (Geneva, chair),
Friedrich Dydak (CERN-EP)
John Ellis (CERN-TH)
Enrique Fernandez (Barcelona)
Helmut Haseroth (CERN-PS)
Vittorio Palladino (Napoli)
Ken Peach (Rutherford Appleton Laboratory)
Michel Spiro (IN2P3, France)
Paolo Strolin (Napoli)

Working Group conveners:
Friedrich Dydak, Juan Jose Gomez-Cadenas (Neutrino oscillations),
Gian Giudice, Andries van der Schaaf (Stopped Muons),
Michelangelo Mangano (DIS),
Gerhard Buchalla (Kaon physics),
Patrick Janot (Higgs factory),
Helmut Haseroth (Neutrino Factory Working Group)
Helge Ravn (Target + Horns)
Horst Schonauer (Accelerator and Compressor)
Roland Garoby (SPL, RF)
Alessandra Lombardi (Cooling studies)

Spokespersons of Experimental R&D :
Friedrich Dydak (HARP), Rob Edgecock (MUSCAT)

The composition and role of this group is an integral part of the package that was submitted to ECFA and endorsed by it. The group is well identified and recognized by the CERN management. The chair (Alain Blondel) was also co-opted in MUG’s first meeting in July 1999, and his mandate renewed in the MUG meeting 31 August until the more formal MCOG structure is in place.

The accelerator group has a direct mandate from CERN and has its own steering committee, to which the MUG chair is frequently invited. The leader is Helmut Haseroth. R&D for high intensity proton source and neutrino factory is supported and funded at CERN, as described in CERN's medium term plan (MTP).
 

Towards the creation of a collaboration for research and development towards a European Neutrino Factory Complex:

It is now proposed to develop a collaborative effort to undertake the accelerator R&D programme at the theoretical, engineering and experimental levels. The first step, as already discussed over the last year at the initiative of the CERN management, is to assemble a European Muon Concertation and Oversight Committee. The first task of this committee will be to review the status of R&D studies and plans and of the more or less formal collaborations that have already taken place, and to establish a fist set of basic goals. It is proposed that two persons (one representative and one surrogate) of the major participating laboratories and funding agencies be nominated for a first meeting to be still convened this year. An organisational structure should be discussed and proposed to the relevant authorities. Representatives of France (IN2P3, CEA), Germany (DESY, GSI), Italy (INFN), Switzerland (PSI) and UK (PPARC,UK) have been approached.
A summary of existing collaborations is given in appendix 1.

Working groups activities

1 The Neutrino Factory Working Group (NFWG) was mandated in spring 1999 by CERN, under the leadership of Helmut Haseroth. This group has issued a status report and working plan last year that is described in NUFACT note 28. The goals and aims of this group is to study the feasibility of a neutrino factory complex at CERN.
    There are several working subgroups in this framework :

    The SPL team, led by Roland Garoby. This team has produced recently a conceptual design report, including a costing of this powerful proton machine. This effort involves collaborations in Europe, for instance with IN2P3 and CEA in France and with LNL and INFN in Italy. An agreement is under negotiation with CEA for the construction and installation at CERN of a 4 MeV high intensity proton source.

    The accumulator and compressor working group, led by Horst Schonauer. This group is collaborating in particular with Rutherford Lab.

    The target and pion collection team led by Helge Ravn. This group participates in the E951 collaboration in Brookhaven (USA), where liquid mercury jets have been succesfully exposed to intense proton bunches. Higher peak intensities should be available at ISOLDE and the group is preparing tests on this facility. Collaboration with Lausanne (laboratoire d'hydrodynamique) and Grenoble (laboratoire de champs intenses), where liquid mercury jets are being tested in high intensity magnetic 20T.
    Horn studies are also well started, with a prototype horn being build and a test laboratory being set-up. High current studies are planned for the end of 2002 and should be followed by 50 Hz repetition rate studies.

    The muon front end group, led by Alessandra Lombardi, which has designed a collection scheme with low frequency RF systems, matched to the SPL. This group is very active in the area of ionization cooling and in the preparation work towards a muon cooling experiment. A test cavity is being prepared to test the gradient achievable in a 88 MHz cavity fitted with a focusing solenoid. Collaboration with UK, INFN, and others is rapidly growing. (see below for the cooling experiment)

    Although this is not as formalised as the ones above, work is taking place on the muon acceleration and storage ring design, thanks to E. Keil and A. Verdier. The INFN Frascati laboratory has recently begun to work on this subject.

    The NFWG holds regular meetings (every two weeks about) that experimental particle physicists also attend regularly.

    2. Physics Working Groups, are working under the sponsorship of ECFA. The goal and purpose of these working groups is to establish the physics opportunities offered by a European Neutrino Factory Complex. These working groups are :

The Neutrino Oscillations Working Group, convened by Friedrich Dydak and Juan Jose Gomez Cadenas. This group has established the uniqueness of the neutrino factory in providing high energy electron neutrino beams, which will allow oscillation experiments to measure very precisely the neutrino mass splitting, mixing parameters and possibly leptonic CP violation, if the oscillation parameters chosen by nature will make it measurable. Some detector concepts are being discussed for this: Li-Ar TPCs (Icarus), a Large Magnetized-Iron Detector (LMD) and more. The  LMD in particular is receiving much attention. Recently, contacts have been made with the Monolith collaboration to promote study of a LMD for experiments on atmospheric neutrinos first and NuFact neutrinos later;  A workshop will be organised on this subject in November 2001, under the co-ordination of Enrique Fernandez (Barcelona). A study of the physics case of a conventional low energy muon neutrino superbeam from the SPL alone has begun with very interesting results. A workshop on this topic will also be organized at CERN in January 2002 under the coordination of Michel Spiro (Saclay), in international collaboration.

The low energy muon working group, convened by Gian Giudice and Andries Van der Schaaf. This group has emphasised the great interest of lepton flavor violating processes like rare muon decays or muon conversion. It now needs to work, in conjunction with experts in the field, on the conceptual designs of the possible slow muon targets, beams and experiments. A significant contribution of this group has been to reveal the potential synergy between the availability of a large flux of muons with the improved production of radioactive nuclei that one can expect with the SPL.

The Kaon physics working group, convened by Gerhard Buchalla, studying the interest of high intensity kaon beams. One major issue here is that this requires that the energy of the proton driver be above 15 GeV, or that a substantial fraction of the protons from SPL is accelerated up to this energy or higher.

The high intensity neutrino physics group, convened by Michelangelo Mangano, studying the opportunities in QCD and electroweak physics offered by the huge neutrino fluxes available in the near vicinity of the muon storage ring of a high energy neutrino factory complex.

The Higgs Factory working group convened by Patrick Janot, studying the physics benefits of medium energy muon colliders, generically at center-of-mass energies equal to the Higgs boson(s) masses to take advantage of direct s-channel production of Higgs and of the unique energy resolution and calibration of muon machines. Muon colliders are a step further in difficulty with respect to the neutrino factory, but it is felt important to keep in mind this important possible extension when discussing the designs.

The present status of these physics and accelerator studies will be summarised in a CERN-ECFA yellow report in preparation. Several of the groups have published their reports as preprints already.
 

3. R&D experiments that are now taking place:

3a. HARP, a hadron production experiment at the CERN PS, to perform precision measurements of particle production over the full solid angles for hadronic projectiles of momenta from 2 to 15 GeV/c on various targets. The spokesperson is Friedrich Dydak. The improved knowledge of particle production is strategically decisive for the neutrino factory complex: the choice of the energy of its proton driver, the design of its target and its collection system. The experiment is fully complete and takes data since August 2001. The experiment in approved to run in 2002.  It will also improve the predictions of neutrino fluxes in detectors of atmospheric neutrinos and of conventional neutrino beams. Extension of these measurements to higher energies for these purposes using the NA49 apparatus has been proposed as well, under the spokespersonship of Giles Barr.

3b The MUSCAT experiment at TRIUMF(Canada), spokesperson Rob Edgecock, is set to measure the poorly known tails of multiple scattering of muons at low energies. These properties are important for muon ionization cooling. The experiment had a technical run in 2000 and will take data in end 2001 and 2002.

These experiments are a good example of the participation of experimental physicists in the practical efforts towards a European Neutrino Factory Complex. It is generally agreed that this should be a strong point also of the future R&D efforts, in particular of the muon cooling demonstration experiment that is being actively prepared in international collaboration.
 

PROJECTS IN PREPARATION

  1. The first project is to complete a YELLOW REPORT describing the status of accelerator studies and the physics case for the numerous possibilities offered by a Neutrino Factory Complex.
  2. On a longer time scale the aim of the studies as defined in MUG in agreement with the CERN management  is to have a Conceptual Design Report for a European Neutrino Factory Complex by  2005-2006. This date is chosen to allow sufficient time for the international decision process that should lead to the beginning of construction as soon as LHC financement is completed, i.e. in 2009-2010. In this way, by 2007, CERN would have two valid options for the future: CLIC and a Neutrino Factory Complex.
  3. An earlier construction date for the proton driver (SPL + accumulator & compressor rings) is conceivable and, of course highly desirable. The SPL, targetry and horn R&D have therefore received the highest priority.
  4. INTERNATIONAL COOLING EXPERIMENT. Cooling is on the critical path for the neutrino factory itself. There is a consensus that a cooling experiment is a necessity. A majority considers it to be the next priority.  A collaboration towards and International cooling experiment has been established with the muon collaboration in United States and a few japanese groups. There is a large interest from European groups in this experiment. A letter of intent to be submitted 15 November is being prepared for PSI and RAL.  The goal is to expose a section of the cooling channel to a muon beam by in 2005. The summary and (preliminary) list of participating institutions in the project is given in appendix 2.
  5. LARGE MAGNETIC DETECTOR. This is the baseline detector for oscillation experiments at the Neutrino factory. Its capability of selecting muon of the proper sign makes it the most promising tool for the full investigation of the golden transition of electron neutrinos and antineutrinos to muon neutrinos. It has been meanwhile realized that it is also a very good detector for atmospheric neutrinos, the muon sign measurement offering some additional sensitivity to matter effects. This makes the HARP effort and its proposed extension to higher energy even more justified. Optimization of a large magnetic detector in the 100 kton mass range could require substantial R&D. In synergy with the Monolith collaboration, it is planned to hold a workshop in Barcelona on the subject in November 9-11 of 2001 to launch these studies. Enrique Fernandez is co-ordinating the organization of this workshop.
  6. LOW ENERGY NEUTRINO SUPERBEAM. The realization that one could already perform an interesting neutrino oscillation experiment with the neutrino beam generated in a conventional way with the 2.2 GeV proton beam from SPL has triggered great interest. The baseline detector is a very large water Cerenkov detector, such as the half Megaton option discussed by the proto-collaboration UNO, but large liquid argon or scintillator detectors are also considered. These large detectors would also make possible a new powerful attack to the existing limits on proton decay and a deeper insight into the nature of the atmospheric neutrino anomaly, and constitute a good detector for the beta-decay neutrino beam recently suggested. An international workshop will be organised at CERN in January 2002 to explore this possibility, which greatly enhances the attractiveness of SPL. This initiative has the great virtue of bringing new players in the game. Michel Spiro will coordinate the organisation of this workshop on our side, in collaboration with the UNO collaboration.


CONCLUSIONS

An ECFA  working group on the future of accelerator-based  High Energy Physics in Europe has recently issued the following recommendations [ECFA/01/213, 6 september 2001].
[...]
4) an improved educational programme in the field of accelerator physics and increased support for accelerator R&D activity in European universities, national facilities and CERN;
[...]
5) a co-ordinated collaborative R&D effort to determine the feasibility and practical design of a neutrino factory based on a muon storage ring.
[...]
We believe that our programme of projects fits closely with the ECFA recommendations. As one can see there is a flurry of initiatives that have been taken and a flurry of initiatives to come. This wide range of projects of reasonable size is very attractive, both because of the novelty offered by the R&D itself and for the prospects offered by working in collaboration towards an exciting programme of experimental investigations and discoveries.
.

Alain Blondel
 

APPENDIX 1 Ongoing Collaborations

SPL :  INFN Legnaro, CEA Saclay, ITEP Moscow

Recirculator and accumulator:  RAL

Target: BNL, EPFL Lausanne, Grenoble

Horns: Uni Crakow, discussions with France

Phase rotation and cooling:
INFN Frascati,
RAL
Mucool collaboration (IIT chicago, Fermilab, BNL, etc.. )
KEK, Uni Osaka
Consortium of European universities (EuNuFact incl Uni.Geneva)
PSI

RLA and Storage ring: Fermilab, INFN frascati

HARP (24 Institutes)     Bari University ,  CERN ,  Dubna JINR ,  Dortmund University ,  Ferrara University ,  Geneve University ,  P.N. Lebedev Physical Institute ,  Legnaro /INFN ,  Louvain-la-Neuve  UCL ,  Milano University/INFN ,  Moscow INR ,  Napoli University/INFN ,  Oxford University ,  Padova University/INFN , Protvino IHEP, Protvino ,  Paris VI-VII University ,  RAL ,  Roma I University/INFN, Roma Tre University/INFN ,  Sheffield University ,  Sofia  Academy of Sciences ,  Sofia  University ,  Trieste         University/INFN ,  Valencia University
 

MUSCAT (10 Institutes) Birmingham, BNL, CERN, Imperial College London, Oxford University, RAL, Riken, Tohoku, Triumf, UCLA.

International Muon Ionization Cooling Experiment (around 38 Institutes, see below)
 
 
 

APPENDIX 2 An International Muon Ionization Cooling Experiment
Letter of Intent,  An International Muon Ionization Cooling Experiment

Summary

A neutrino factory based on a muon storage ring is the ultimate tool for studies of neutrino oscillations, including possibly leptonic CP violation. It is also the first step towards mu+mu- colliders. Ionisation cooling of muons constitutes an important ingredient of the performance and cost of a neutrino factory, but has never been realised in practice. This motivates a programme of R&D at international level, including an experimental demonstration. The aims of this muon ionisation cooling experiment are as follows:
a) to show that one can design, engineer and build a section of cooling channel capable of giving the desired performance for a neutrino factory;
b) to place it in a muon beam and measure its performance in a variety of modes of operation and beam conditions.
The concept of a muon ionization cooling experiment has been extensively studied, and an international collaboration is set-up to realize it. A section of a cooling channel assembles liquid hydrogen absorbers providing energy loss, combined with high gradient RF cavities to re-accelerate the particles, the ensemble being tightly contained in a magnetic channel. Spectrometers placed before and after the cooling section perform the measurements of emittance reduction and transmission. It appears feasible to build a section of cooling channel that reduces the emittance of a muon beam by 5-10%, and to measure this cooling factor with a precision of 10-3.
This letter of intent describes the principle of the measurements, the experimental set-up, the requirements on beam properties, the expected schedule and estimated cost of the experiment, and the requirements on infrastructure. Technical help from the host laboratory is requested in preparation of a technical proposal, to refine the layout and implantation of this experimental facility, and to study the safety issues related to hydrogen absorbers and to the intense magnetic fields.
 
 
 

International Muon Ionization Cooling Experiment
 

Steering committee:
A. Blondel* (University of Geneva)
H. Haseroth (CERN**)
R. Edgecock (Rutherford Appleton Laboratory)
Y. Kuno (Osaka University)
S. Geer (FNAL)
D. Kaplan (Illinois Institute of Technology)
M. Zisman (Lawrence Berkeley Laboratory)
* convener for one year (June 2001-2002)

Conveners of Technical teams:

a) Concept development and simulations:
 Alessandra Lombardi (CERN **)
 Panagiotis Spentzouris (FNAL)
 Robert B Palmer (BNL)

 b) Hydrogen absorbers:
 Shigeru Ishimoto (KEK)
 Mary-Anne Cummings (Northern Illinois)

 c) RF cavities and power sources
 Bob Rimmer (LBNL)
 Roland Garoby (CERN**)

 d) Magnets
 Mike Green (LBNL)
 Jean-Michel Rey (CEA Saclay)

 e) Particle detectors
 Vittorio Palladino (INFN Napoli)
 Alan Bross (FNAL)

 f) Beam lines
 Rob Edgecock (RAL)
 Claude Petitjean (PSI)

 g) RF radiation
 Jim Norem (Argonne)
 Ed McKigney (IC London)
 
 

** pending the review of CERN activities in accelerator R&D which will
take place in the framework of the LHC cost-to-completion analysis.

So far incomplete and preliminary list of
Participating institutes

INFN:  Bari, Milano, Padova, Napoli, Roma I  Roma II, Roma III
LNF Frascati, LNL Legnaro

Rutherford Appleton Laboratory  RAL
University of Oxford, Imperial College London

DAPNIA, CEA Saclay

Louvain La Neuve

NESTOR institute, University of Athens, Hellenic Open University

CERN** (H. Haseroth)
** pending the review of CERN activities in accelerator R&D which will take place in the framework of the LHC cost-to-completion analysis.

University of Geneva, University of Zurich, ETH Zurich
Paul Scherrer Institute PSI

KEK
Osaka University

Argonne National Laboratory
Brookhaven National Laboratory
Fermi National Accelerator Laboratory
Lawrence Berkeley National Laboratory

University of California Los Angeles, University of Mississippi, University of Indiana,
Princeton University, University of Illinois, Michigan State University, Northern Illinois University,
Illinois Institute of Technology, …….