MICE-CONF-GEN-121 MICE: The International Muon Ionization 6 Cooling Experiment 0 0 2 Daniel M. Kaplan n a J IllinoisInstituteofTechnology,Chicago,Illinois60616,USA 9 1 (fortheMICECollaboration) ] h p Abstract. Ionizationcoolingofa muonbeamisa keytechniquefora NeutrinoFactoryorMuon - Collider.Aninternationalcollaborationismountinganexperimenttodemonstratemuonionization c coolingattheRutherfordAppletonLaboratory.Weaimtocompletetheexperimentby2010. c a . s c INTRODUCTION i s y h The experimental establishment of neutrino oscillations [1] has stimulated widespread p interestinamuonstoragering-basedNeutrinoFactory[2],possiblytheultimatetoolfor [ studying the neutrino mixing matrix [3]. Two feasibility studies [4, 5] have shown that 1 ahigh-performanceNeutrinoFactorycan bebuiltusingavailabletechnology.However, v some of the beam-manipulation techniques envisaged have yet to be applied in prac- 6 4 tice. Of these, ionization cooling of the muon beam [6, 7] is perhaps the most novel. 1 In the longer term it holds the promise of s-channel Higgs Factories and multi-TeV 1 0 muon-antimuon colliders, with potential for unique studies of matter and energy at the 6 most fundamental level [8], complementing those at the Large Hadron Collider and the 0 proposedInternationalLinearCollider. / s Ionization cooling contributes significantly to both the performance (up to a factor c i of 10 in intensity [9]) and cost (as much as 20% [5]) of a Neutrino Factory. This s y motivatestheMuonIonizationCoolingExperiment(MICE).MICEisintendednotonly h to demonstrate the principle of ionization cooling, but (and perhaps more importantly) p toshowhowtobuildandoperateadevicewiththeperformancerequiredforaNeutrino : v Factory. The experience gained from MICE will provideinput to the final design of the i X NeutrinoFactorycoolingchannelandfirmupitscostestimate.Animportantpartofthe r MICE program is to study the cooling process by varying the relevant parameters, so a thatan extrapolationcanbemadetoadifferentcooling-channeldesign,e.g.,aring[10] orhelical coolingchannel[11], shouldoneofthesebeshowntobeadvantageous. During 2001 and 2002, the international MICE Collaboration [12] was formed and developed a proposal [13] to carry out this program using a muon beam produced with the ISIS accelerator at Rutherford Appleton Laboratory (RAL). The proposal was approved in 2003. The MICE collaboration includes accelerator and experimental particle physicists from Europe, Japan, and the US. As of this writing, funding for the firstphaseofMICEhas beenprovidedinItaly,Japan,theNetherlands,Switzerland, the UK,and theUS. Weaimfora definitivedemonstrationofionizationcoolingby2010. DESIGN OF THE EXPERIMENT The MICE design is presented in detail in the proposal [13] and Technical Reference Document(TRD) [14], and isbriefly summarizedhere. ThegoalsofMICE are • to engineer and build a section of cooling channel (of a design that can give the desired performance for a Neutrino Factory) that is long enough to provide a measurable(≈10%) coolingeffect, butshortenoughto bemoderatein cost;and • to measure the resulting cooling effect with an absolute accuracy of 0.1% over a muon-beammomentumrange of140–240MeV/c. ThelayoutofMICEisshowninFig.1.Thetracksofsinglemuonsthroughtheappara- tuswillbemeasuredusingstandardparticle-physicstechniques,sincebunched-beamdi- agnosticslack theneeded precision. The5.5m-longcooling section,consistingofthree absorbers and eight rf cavities encircled by lattice solenoids, is therefore surrounded at each endby trackingdetectors,tomeasurebeamemittanceat theentrance andexit,and particle-ID detectors to reject particles other than muons. This requires the placement of tracking detectors close to the rf cavities and is therefore sensitive to backgrounds causedbydark-currentelectronsandtheirassociatedx-rays.Improvingourunderstand- ing of such backgrounds is essential to the successful planning and execution of MICE andisamuch-anticipatedresultfromupcomingtestsbytheMuCoolCollaboration[15]. The cooling section is one lattice cell of the “SFOFO” cooling channel developed in Feasibility Study II [5] (with minor modifications to reduce cost and comply with RALsafetyrequirements),withafullabsorberat eachend toprotectthedetectorsfrom rf-cavity emissions. This arrangement provides considerable flexibility, as the solenoid polarities and currents can be varied to test a variety of lattices. Provision will be made for a variety of solid absorbers as well as liquid hydrogen and helium. (In principle, someothercoolingcell couldalso betested,perhaps inasubsequentMICE phase.) Figure 2 shows the simulated effect of the cooling section on the normalized transverse beam emittance, as well as the beam transmission, vs. that emittance, for 200MeV/c average beam momentum and nominal optics settings of the SFOFO lattice cell (3.2T maximum on-axis field). For input emittance below the equilibriumvalue of 2p mm·rad the beam is heated; above 6p mm·rad scraping begins to deplete the beam. The detailed comparison of such measurements against Monte Carlo predictions, for a variety of beam momenta, emittances, and apparatus configurations, will serve to validate our Monte Carlo and design approach and allow extrapolation to the longer (∼100m)coolingchannelstypicallyusedin NeutrinoFactorydesigns. Achieving 0.1% emittance resolution will require careful calibration and simulation. Scattering of the beam in the detectors causes a correctable bias, as illustrated (for input-beamemittancee =2.5p mm·rad)inFig.3[16]:beforecorrection,thetransverse t emittance measured in each spectrometer is ∼1% larger than the “true” emittance. The goal of 0.1% emittance measurement will thus require that this bias be calibrated and FIGURE1. Three-dimensionalcutawayrenderingoftheMICEapparatus.Themuonbeamentersfrom the lower left and is measured by time-of-flight (TOF) and Cherenkov detectors and a first solenoidal trackingspectrometer.Itthenentersthecoolingsection,whereitisalternatelysloweddowninabsorbers andreacceleratedbyrfcavities,whilebeingfocusedbyalatticeofsuperconductingsolenoids.Finallyitis remeasuredbyasecondsolenoidaltrackingspectrometeranditsmuonidentityconfirmedbyCherenkov andTOFdetectorsandacalorimeter. EQUILIBRIUM EMITTANCE FIGURE 2. (Left) percent change of normalized transverse emittance and (right) beam transmission throughcoolingsection,bothvs.inputemittanceinp mm·rad. corrected to∼10% ofitself(to beverified bycalibrationruns withnocoolingsection). Tracking detectors To minimize beam scattering and sensitivity to x-rays, the tracking detectors will be thin(350m m-diameter)scintillatingfibers,gangedbysevenstoreducetheneededelec- tronics channel count. Each group of seven adjacent fibers is mated to a 1mm clear light-guidefiber that conveys the scintillation light to a VLPC photosensor. The >85% quantum efficiency of the VLPCs [17] results in an average of 11 photoelectrons per (cid:30)(cid:4)(cid:1) (cid:0) (cid:1) FIGURE3. Resolutioninuncorrectedemittance(for2.5p mm·radinputemittance)ina)upstreamand b)downstreamspectrometer. minimum-ionizing particle, as verified in cosmic-ray tests [16]. As in the D0 experi- ment [17], the use of two staggered layers per view ensures high efficiency. Each spec- trometer will be made up of five detector stations, each with three views arranged in ◦ 120 stereo, deployed within a 1.1m-long 4T superconducting solenoid. A prototype 4-stationdetectorisnowundergoingbeam testsina1T solenoidat KEK. Particle identification The muon beam may contain residual pions which are transported through the large momentum acceptance of the beamline, as well as electrons from the in-flight decay of muons. A three-plane time-of-flight system provides the precise time information needed for particle identification, emittance measurement, and off-line bunch construc- tionandtimingwithrespecttotherfphase.Additionalparticleidentificationisprovided beforeand afterthecoolingchannelby Cherenkovdetectors and acalorimeter. STAGING AND CURRENT STATUS Theneedtocarefullycross-calibratethespectrometersaswellasthecostofthecooling sectionsuggeststagingtheinstallationandoperationofMICEasindicatedinFig.4.The currently funded first phase of MICE includes the detectors but not thecooling section; thesecond phasewill beassembled in stepsas funds allow.At present thefirst rf cavity is under test in the MuCool Test Area at Fermilab, the Absorber/Focus-Coil and RF- cavity/Coupling-Coilmoduledesignsare welladvanced, and work is inprogress on the spectrometers,beamline,andinfrastructure. First beamis plannedforApril2007. FIGURE4. SixpossiblestepsinthedevelopmentofMICE. ACKNOWLEDGEMENTS TheauthorgratefullyacknowledgessupportoftheUSMICEinstitutionsbytheDepart- mentofEnergyand theNationalScience Foundation. REFERENCES 1. Y.Fukudaetal.,Phys.Lett.B433,9(1998);ibid.436,33(1998);Phys.Rev.Lett.81,1562(1998); ibid.82,2644(1999);Q.R.Ahmadetal.,ibid.87,071301(2001);ibid.89,011301(2002);ibid. 89,011302(2002). 2. 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