Besides continued work on the parameters of a 3-4 and 0.5 TeV CoM collider,
many studies are now concentrating on a machine near 100 GeV that could be a
factory for the s-channel production of Higgs particles. We mention the
research on the various components in such muon colliders, starting from the
proton accelerator needed to generate pions from a heavy-Z target and
proceeding through the phase rotation and decay channel, muon cooling,
acceleration, storage in a ring and the collider detector. We also mention
theoretical and experimental R&D plans for the next several years that should
lead to a better understanding of the design and feasibility issues for all of
the components. This note is a summary of a report updating the progress on the
R&D since the Feasibility Study of Muon Colliders presented at the Workshop
Snowmass'96.Comment: 3 pages, 2 figures, LaTex EPAC format; to be published Proceedings of
  the EPAC98 Conference, Stockholm, Sweden, June 1998. Additional information
  and articles at http://www.cap.bnl.gov/mumu

Collaboration, Muon Collider

Gallardo, J.

Palmer, R.

Sessler, A.

Tollestrup, A.

English

arXiv

Besides continued work on the parameters of a 3--4 and 0.5 TeV center of mass (CoM) collider, many studies are now concentrating on a machine near 100 GeV (CoM) that could be a factor for the s-channel production of Higgs particles. The authors mention the research on the various components in such muon colliders, starting from the proton accelerator needed to generate pions from a heavy-Z target and proceeding through the phase rotation and decay ({pi} {r_arrow} {mu}{nu}{sub {mu}}) channel, muon cooling, acceleration, storage in a collider ring and the collider detector. The authors also mention theoretical and experimental R and D plans for the next several years that should lead to a better understanding of the design and feasibility issues for all of the components. This note is a summary of a report updating the progress on the R and D since the Feasibility Study of Muon Colliders presented at the Workshop Snowmass `96

UNT Digital Library

Muon collider overview: Progress and future plans

Besides continued work on the parameters of a 3-4 and 0.5 TeV center of mass (COM) collider, many studies are now concentrating on a machine near 100 GeV (COM) that could be a factory for the s-channel production of Higgs particles. We mention the research on the various com- ponents in such muon colliders, starting from the proton accelerator needed to generate pions from a heavy-Z tar- get and proceeding through the phase rotation and decay ({pi}{yields}{mu}{nu}{mu}) channel, muon cooling, acceleration storage in a collider ring and the collider detector. We also men- tion theoretical and experimental R & D plans for the next several years that should lead to a better understanding of the design and feasibility issues for all of the components. This note is a summary of a report[l] updating the progress on the R & D since the Feasibility Study of Muon Colliders presented at the Workshop Snowmass'96.[2

LBNL-42090 Muon Collider Overview: Progress and Future Plans R. Palmer, A. Tollestrup, J. Gallardo, and A.M. Sessler Accelerator and Fusion Research Division June 1998 Presented at the Sixth European Particle Accelerator Conference (EPAC Y8), Stockholm, Sweden, June 22-26,1998, and to be published in the Proceedings DISCLAIMER This document was prepared as an account of work sponsored by t h e  United States Government. While this document is believed to contain correct information, neither the United States Government nor any  agency thereof, nor The Regents of the University of California, nor a n y  of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, o r  service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or The Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of t h e  United States Government or any agency thereof. or The Regents of the University of California. Ernest Orlando Lawrence Berkeley National Laboratory is an equal opportunity employer. DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. LBNL-42090 BNL - 65627 CBP Note-263 Muon Collider Overview: Progress and Future Plans" . -  R. Palmer, A. Tollestrup and J. Gallardo Brookhaven National Laboratory Upton, NY 11973 USA A.M. Sessler Ernest Orlando Lawrence Berkeley National Laboratory Berkeley, CA 94720 USA June 1998 * This work was supported by the Director, Office of Energy Research, Office of High Energy and Nuclear Physics, Division of High Energy Physics, of the U.S. Department of Energy under Contract Nos. DE-AC 03- 76SF00098 and DE-AC02-76CH000 16. Muon CoUider Overview: Progress and Future Plans R. Palmer, A. Sessler, A. Tollestrup and J. Gallardo for the Muon Collider Collaboration, BNL, New York, USA 100 GeV 'First Muon Collide?, the exact energy taken to Abstract be representative of the actual mass of a Higgs particle. Besides continued work on the parameters of a 3 4  and 0.5 TeV center of mass (CoM) collider, many studies are now concentrating on a machine near 100 GeV (CoM) that could be a factory for the s-channel production of Higgs particles. We mention the research on the various com- ponents in such muon colliders, starting from the proton accelerator needed to generate pions from a heavy-2 tar- get and proceeding through the phase rotation and decay (II. -+ pv,,) channel, muon cooling, acceleration, storage in a collider ring and the collider detector. We also men- tion theoretical and experimental R & D plans for the next several years that should lead to a better understanding of the design and feasibility issues for all of the components. This note is a summaty of a report[ 11 updating the progress on the R & D since the Feasibility Study of Muon Colliders presented at the Workshop Snowmass'96.[2] 1 INTRODUCTIQN 2 COMPONENTS Proton Driver The specification of the proton driver for the three machines is assumed the same: lOI4 pm- tondpulse at an energy above 16 GeV and 1-2 ns rms bunch lengths. There have been three studies of how to achieve them. The most conservative, at 30 GeV, is a generic de- sign. Upgrades of the FN& (at 16 Gev) and BNL (at 24 GeV) accelerators have also been studied. Despite the very short bunch requirement, each study has concluded that the specification is attainable. Experiments have been done and are @&ed to confirm some aspects of these designs. [ 31 z \ Unlike protons, muons are point like but, unlike electrons, fore, can be accelerated and collided in rings. As a result, than either a proton or electron machine. A 3 TeV muon collider (with effective energy comparable with that of an SSC) would fit on existing sites, such as BNL or FNAL (see Figs. 1, 2). Another advantage resulting from the low synchrotron radiation is the lack of beamstrahlung and the possibility of very small collision energy spreads. A beam energy of AE?E of 0.003 % (equivalent 1-0 a CoM spread of A m  of 0.002 96) is considered feasible for a 100 GeV \ \ / I I they emit relatively little synchrotron radiation and there- a muon collider with a given energy reach could be smaller / / / / \ \ / / / / \ \ \ 1 ' 1kUI +----+ ' / \ / \ / / ' / machine; and it has been shown that by observing spin precession, the absolute energy could be determined to a \ ' \ '  \ /  small fraction of this width. These features become impor- tant in conjuction with the large s-channel Higgs produc- tion (p+p- -+ h, 43000 times larger than for e+e- + h), allowing precision measurements of the Higgs mass, width Figure 1: Plan of a 3 TeV Muon Collider shown on the FPAL site as an example. and branching ratios. Such machines are clearly desirable. The questions are: e whether they can be built and physics done with e what will they cost. them Much progress has been made in addressing the first ques- tion and the answer, so far, appears to be positive. It is too early yet to address the second. We have studied ma- chines with center of mass energies of 100 GeV, 400 GeV and 3 TeV, defined parameters and simulated many of their components (see Tb.l). Most work has been done on the 100 rn - Figure 2: Plan of a lo0 GeV CoM Muon Collider. Muon Prodimction Pion production has been taken from the best models available, but an experiment (BNL- E910) that has taken data, and is W i g  analyzed, will re- fine these m&ls.[4] The assumed 20 T capture solenoid appears to be well within current technology (a coil with the specified field and aperture is now nearing completion at the National High Magnetic Reld Laboratory, Florida State University). Capture, decay and phase rotation have been simulated, and have achieved the specified production of 0.3 m u m  per initial proton. The most Serious remaining questions for this part of the machine are: 1. The nature and material of the target: ”he base- line assumption is that a liquid metal jet will be used, but the efiects of shack heating by the beam, and of the eddy cillTentS induced in the liquid as it enters the solenoid, are not yet fully understood. 2. The maximum RF field in the phase rotation. For the short pulses used, the current assumptions would be reasonably conservative under normal operating conditions., but the effects of the massive radiation from the nearby target are not known. Both these questions can be answered in a target experi- ment plauned to be performed within the next two years at AGS 451 Cooling The required ionization cooling is the most difficuit and least understood element in any of the muon colliders studied. Ionization cooling is a phenomenon that occurs whenever there is energy loss in a strong focus- ing environmerit. Such an environment has existed, for instance, in the iron toroid muon calorimeters of several neutrino experiments, and a Monte Carlo simulation has shown[q that amling mmt have occured there. But achiev- ing the nearly lo6 reduction required is a challenge. Cool- ing over a wide range has been simulated using lithium lenses and ideal1 (hear matrix) matching and acceleration; and examples of limited sections of solenoid lattices with realistic accelerating fields have now been simulated. But the specification and simulation of a complete system has not yet been done. Much theoretical work remains space charge and wake fields must be included, lattices at the start and end of the cooling sequences must be design&, lattices including liquid lithium lenses must be designed and studied, and the sections must be matched together and simulated as a full sequence. The tools for this work are nearly ready, and this project should be completed within Technically, lone of the most challenging aspects of the High gradlient Rl? (e.g. 36 MV/m at 805 MHz) oper- ating in strong (5-10 T) magnetic field, with beryllium foils between the cavities. two Y=.m cooling system appear to be: An experiment is planned that will test such a cavity, in the required ‘fields, in about two years time. On an approxi- mately six year time scale, a “Cooling Test Facility” is be- ing proposed that could test ten meter lengths of Merent cooling systems.[8] If they are required, there is the need to develop: Lithium Lenses: (e.g. 2 cm diameter, 70 cm long, liquid lithium lenses with 10 T surface fields and a repe4ition rate of 15 Hz). They may not be needed for the low energy “First Muon Collidef‘, which would ease the urgency of this rather long term R & D. Meanwhile a short lithium lens is under con- struction at BINP (Novosibirsk, Russia). Acceleration The acceleration systems are probably the least controversial, although possibly the most expen- sive, part of a muon collider. Reh ina ry  parameters have been specified for acceIeration sequences for a 100 GeV and 3 TeV machines, but they need refinement. In the low energy case a linac is followed by three recirculathg ac- celerators. In the high energy accelerator, the recirculat- chrotrons emploqiing Bltemting pulsed and superconduct- ing magnets. The parameters do not appear to be extreme, and it does not appear as if serious problems are likely. ing ~c~elerators are followed by three €St ramping SP- CoUider The collider lattices are challenging because of their required very low intersection betas, high single bunch intensities, and short bunch lengths (see Tb. 1); how- ever, the fact that all muons will decay after about lo00 tums means that slowly developing instability are not a problem. Feasibility lattices have been generated for a 4 TeV case, and more detailed designs for 100 GeV ma- chines studied. In the latter case, but stili without errors, 5a acceptances in both transverse and longitudinal phase space have been achieved in tracking studies. Beam scrap- ing schemes have been designed for both the low energy (collimators) and high energy (septum extractors) cases. Bunch length and longitudinal stabiIity problems are avoided if the rings, as specified, are sufliciently isochronous, but some rf is needed to remove the impedance generated momentum spread. Transverse in- stabilities (beam breakup) should be controlled by rf BNS The heating of collider ring superconducting magnets by electrons from muon decay can be controlled by thick tung- sten shields, and this technique also shields the space sur- rounding the magnets from the induced radioactivity on the inside of the shield walL A conceptual design of magnets for the low energy machine has been defined. Although much work is yet to be done (inclusion of er- rors, higher order correction, magnet design, rf design, etc), the collider ring do not appear likely to present serious problems. damping. Neutrino Radiation and Detector Background Neu- trino radiation, which ~ t ~ ~ a l l y  rises as the cube of the en- ergy, is not serious for machines with center of mass ener- gies below about 1.5 TeV. It is thus not si@ficant for the 2 m h e  param 3 .  16 4 15 4 2 x 10l2 28 204 6Ooo 500 0.16 1.7 x lo-'' 50 0.3 0.3 3.2 0.043 5 x le4 8 x lOY4 2.5 x 1013 16 16 0.14 1.7 x lo-'* 50 2.3 2.3 24 0.043 1033 8 x First Muon Collider; but above 2 TeV, it sets a constraint on the muon cunent and makes it harder to achieve desired luminosities. However, advances in cooling, and correc- tion of tune shifts may still allow a machine at 10 TeV with substantial luminosity (> ~m-~s- l ) .  Background in the detector was, at first, expected to be a very serious problems. But after much work, shielding systems have evolved that limit most charged hadron, elec- tron, gamma and neutron background to levels that are ex- pected to be acceptable. Muon background, in the higher energy machines, is a special problem that can cause seri- ous fluctuations in calorimeter measu$ments. It has been &own thar fast liming and segmentation c a ~  help suppress this background, and preliminary studies of its effects on a physics experiment are encouraging. The studies are ongoing.[9] 0.12 1.7 x 10-l' 85 4 4 82 0.05 1.2 x 1032 . 8 x 1.6 x lo3 3 SUMMARY Much progress has been made since Snowmass, but much still needs to be done. A time scale of two years should al- low completion of simulation studies, and the experimental testing of crucial technical challenges. Rototype construc- tion and testing will be required for another 4-6 years. The construction of a ' F i t  Muon Collider" by about 20 10 does seem to be possible. 4 ACKNOWLEDGMENTS This research was supported by the U.S. Department of Energy under Contracts No. DE-AC02-98CH10886, DE- AC02-76CH03000 and DE-AC03-76SFWO98. 5 x 1013 2 15 4 4 x 1oI2 1 81 300 10 0.01 1.7 x lo-'' 195 9 9 187 , 0.02 -2  x 1031 7 x  10-5 4 x 103 0.003 1.7 x 10-l' 280 13 13 270 0.015 1031 2 x 10-5 4 x 103 5 REFERENCES [ 1 J Status of the Muon Collider Research and Development and F u t n  Plans, in preparation. [Z] R. B. Palmer, A. Sessler and A. Tollestrup, Proceedings of the I996 DPFDPB Summer Study on High-Eneqy Physics (Stanford Linear Accelexator Center, Menlo Park, CA, 1997) [3] C. Ankenbrandt et al., Bunching Near Transition in the AGS, Fermilab pub-98-06, submitted to Phys. Rev. D. [4] Experiment E-910 at BNL-AGS, available at the URL htlp://www.nevis.columbia.edu/heavyion/e9 1 O/, 1997. [5] K. McDonald, available at the URL http:/~~ep.princeton.eduhnumu/ [6] B. King, available at the URL http://pub web.bnl.gov/people/bking/ [q R. Fernow, ICOOL, Fortran program to simulate muon ion- ization cooling. [SI C. Aukenbrandt et ai., Ionizatwn Cooiing R&D Program for a High Luminosity Muon Collider (MUCOOL Proposal), FNAL.-P904, April 1998; available at the URL http~/~..fnat.gov/projects/muoncollide 191 I. Stumer et ai., Study of Detector Backgrounds in a p+p- Colliakr , Proceedings of the 1996 DPFDPB Summer Study on High-Energy Physics, (Stanford Linear Accelerator Cen- ter, Menlo Park, CA, 1997) 3 

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