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Mu2e Experiment Proposal to Search for ¹¡N ! e¡N with a Single Event Sensitivity Below 10¡16 Mu2e Experiment Fermilab October 10, 2008 The Mu2e Collaboration R.M. Carey, K.R. Lynch, J.P. Miller¤, and B.L. Roberts Boston University, Boston, Massachusetts W.J. Marciano, Y. Semertzidis, and P. Yamin Brookhaven National Laboratory, Upton, New York Yu.G. Kolomensky University of California, Berkeley, California W. Molzon University of California, Irvine, California J.L. Popp City University of New York, New York, New York C.M. Ankenbrandt, R.H. Bernstein¤, D. Bogert, S.J. Brice, D.R. Broemmelsiek, R. Coleman, D.F. DeJongh, S. Geer, D.E. Johnson, R.K. Kutschke, M. Lamm, M.A. Martens, D.V. Neu®er, M. Popovic, E.J. Prebys, R.E. Ray, M.J. Syphers, H.B. White, K. Yonehara, and C.Y. Yoshikawa Fermilab, Batavia, Illinois K.J. Keeter and E. Tatar Idaho State University, Pocatello, Idaho P.T. Debevec, G. Gollin, D.W. Hertzog, and P. Kammel University of Illinois, Urbana-Champaign, Illinois V. Lobashev Institute for Nuclear Research, Moscow, Russia D.M. Kawall and K.S. Kumar University of Massachusetts, Amherst, Massachusetts R.J. Abrams, M.A.C. Cummings, R.P. Johnson, S.A. Kahn, S.A. Korenev, T.J. Roberts, and R.C. Sah Muons, Inc., Batavia, Illinois Andr¶e de Gouv^ea Northwestern University F. Cervelli, R. Carosi, M. Incagli, T. Lomtadze, L. Ristori, F. Scuri, and C. Vannini Istituto Nazionale di Fisica Nucleare Pisa, Universit`a Di Pisa, Pisa, Italy M. Corcoran Rice University, Houston, Texas R.S. Holmes and P.A. Souder Syracuse University, Syracuse, New York M.A. Bychkov, E.C. Dukes, E. Frlez, R.J. Hirosky, A.J. Norman, K.D. Paschke, and D. Po·cani¶c University of Virginia, Charlottesville, Virginia J. Kane College of William & Mary, Williamsburg, Virginia ¤Contactperson Contents Executive Summary xv I Mu2e in Brief 1 1 Theoretical Motivation 3 1.1 Introduction . 3 1.2 Comparison to Current HEP Program . 5 1.2.1 Model Independent Analysis: ¹N ! eN vs. ¹ ! eγ . 5 1.2.2 CLFV and new physics at the TeV scale . 8 1.2.3 CLFV, neutrino masses, and the matter{antimatter asymmetry of the Universe . 13 2 Overview of the Experiment 17 2.1 Experimental Sensitivity . 20 2.2 Experimental Principles . 20 2.3 Proton Beam . 22 2.4 Solenoid System . 24 2.4.1 Production Solenoid . 24 2.4.2 Transport Solenoid . 25 2.4.3 Detector Solenoid . 26 2.5 Stopping Target . 28 2.6 Detector . 28 2.7 Backgrounds . 29 2.7.1 Decay-in-Orbit Electrons . 29 2.7.2 Nuclear Capture of Muons . 30 2.7.3 Radiative pion capture . 30 2.7.4 High energy beam electrons, (» 100 MeV) . 31 2.7.5 Late Arriving Particles . 31 2.7.6 Cosmic Rays . 32 2.8 Phase II: Mu2e at Project X Intensities . 32 v CONTENTS 3 Sensitivity and Backgrounds 35 3.1 Introduction . 35 3.1.1 Underlying Processes and Calculations . 36 3.2 Physics Background Sources . 37 3.2.1 Electrons from Muon Decay in Orbit . 39 3.2.2 Radiative ¹ Capture . 40 3.2.3 Beam Electrons . 43 3.2.4 Muon Decay in Flight . 44 3.2.5 Pion Decay in Flight . 45 3.2.6 Radiative ¼ Capture . 45 3.2.7 Antiproton Induced . 46 3.2.8 Long Transit Time Backgrounds . 50 3.2.9 Cosmic Rays . 51 3.3 Physics Requirements . 52 3.4 Background Level . 52 3.5 Resolution Measurements . 53 3.5.1 Decay-in-Orbit . 53 3.5.2 Extinction Measurement . 58 3.6 Conclusions on the Sensitivity . 59 4 Cost Estimate and Schedule 61 4.1 Cost Estimate . 61 4.2 Schedule . 63 5 R&D Request 65 5.1 Introduction . 65 5.2 Speci¯c R&D Tasks . 65 5.2.1 Solenoid System . 65 5.2.2 Tracker . 66 5.2.3 Extinction System and AC Dipole . 67 5.2.4 Accelerator . 67 5.2.5 Cosmic Ray Shield . 69 5.2.6 Calorimeter . 69 5.2.7 Spectrometer Calibration System . 69 5.3 R&D Cost Estimate . 70 II Mu2e in Detail 71 6 Proton Beam 73 6.1 Overview . 73 6.2 Delivering Protons to the Accumulator . 73 6.3 Momentum Stacking and Rebunching . 76 vi CONTENTS 6.4 Resonant Extraction . 77 6.5 Proton Extinction . 79 6.6 Total Proton Delivery . 82 6.7 Radiation Safety . 83 7 Production Target 85 7.1 Introduction . 85 7.2 Muon Production . 87 7.3 Stopped Muon Yield . 91 7.4 Target Heating . 93 7.5 Target Cooling . 94 7.6 Heat and Radiation Shield . 98 8 Muon Beamline 101 8.1 Collimators . 102 8.2 Absorbers . 103 8.3 Muon Beam Stop . 104 8.4 Vacuum System . 107 9 Production, Transport, and Detector Solenoids 117 10 Detector 125 10.1 Muon Stopping Target . 126 10.2 Muon Capture Monitor . 129 10.2.1 Purpose and Method . 129 10.2.2 Location for the Germanium Detector . 130 10.2.3 Calibration . 131 10.2.4 Selection of Germanium Spectrometer System . 132 10.3 The Tracking Detector . 133 10.3.1 Physics Requirements . 134 10.3.2 Tracking Detector Overview . 135 10.3.3 Tracking Detector Performance . 138 10.3.4 Mechanical Construction . 150 10.3.5 Pad Readout . 151 10.3.6 Drift Gas . 154 10.3.7 An Alternate Design . 154 10.4 Electromagnetic Calorimeter . 155 10.4.1 Calorimeter Description . 157 10.4.2 Crystal Choice . 158 10.4.3 Calorimeter Readout . 161 10.4.4 Calorimeter Cooling . 162 10.4.5 Calorimeter Mechanical Support . 163 10.4.6 Calorimeter Radiation Dose . 164 vii CONTENTS 10.4.7 Calorimeter Performance . 164 10.4.8 Calorimeter Calibration . 164 11 Cosmic Ray Shield 167 11.1 Cosmic Ray Background Rate Calculation . 167 11.2 Beam Induced Rates . 171 11.3 Passive Cosmic Ray Shield . 172 11.4 Active Cosmic Ray Shield . 172 11.5 Scintillator Strips . 175 11.6 Wavelength Shifting Fiber . 175 11.7 Photomultiplier Tube and Signal Response . 176 11.8 Assembly and Installation of a Three-Layer Module . 178 11.9 Calibration of Active CR Shield . 179 12 Trigger & Data Acquisition System 181 12.1 Overview . 181 12.2 Tracker Front End Electronics . 183 12.3 Calorimeter Digitizer Modules . 186 12.4 Level-1 Trigger . 188 12.5 Event Building and Processing . 189 12.6 Slow Control and Monitoring . 191 13 O²ine Computing and Data Analysis 193 14 Detector Enclosure, Civil Construction, and Infrastructure 195 14.1 Beamline . 195 14.2 Detector Enclosure . 196 14.3 Electrical Power . 199 14.4 Cryogenics . 199 15 Environment, Safety and Health 203 15.1 Antiproton Accumulator and Debuncher Rings . ..
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