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A High-Sensitivity Search for Charged Lepton Flavor at Fermilab

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A High-Sensitivity Search for Charged Lepton Flavor at Fermilab Mu2e: A High-Sensitivity Search for Charged Lepton Flavor at Fermilab E. Craig Dukes University of Virginia The 11th International Workshop on Tau Lepton Physics September 13, 2010 Is the Large Hadron Collider the Last in a Long Line of ever Higher Energy Particle Accelerators? Presently there are no concrete plans for an accelerator to probe the next energy regime How are we going go probe higher mass scales without higher energies? We will be forced to abandon exploiting Einstein’s mass- energy relation, E=mc2, and rely more and more on Heisenberg’s uncertainty principle, DEDt ≳ ħ/2: rare and precision physics E. Craig Dukes Tau2010 / Mu2e: Lepton Flavor Violation 2 Why Search for Charged Lepton Flavor Violation? N e N' • In Standard Model not there neutrino mass discovery implies an unobservable 10-52 rate Lepton flavor conservation accidental • Hence, any signal unambiguous evidence of new physics in the extended Standard Model • Exquisite sensitivities can be obtained experimentally sensitivities that allow favored beyond-the-standard-model theories to be tested Many models explaining the neutrinoNewSupersymmetry heavymass hierarchy neutrino produce N → eN at levels that will be probed by Mu2e E. Craig Dukes Tau2010 / Mu2e: Lepton Flavor Violation 3 History of Lepton Flavor Violation Searches Muon established as independent lepton in 1947 as →eg not seen 19 Number of muons needed:Feinberg ~5x10 1958 loop calculation: Number of grains of sand on Earth:→ 7.5x10eg must18 be 10-4-10-5 Non-observation of →eg implies two neutrinos Present limit constraining New Mu2e at Fermilab Physics theories intends to improve sensitivity by ~10,000 and then up to ~100,000 with Project X! E. Craig Dukes Tau2010 / Mu2e: Lepton Flavor Violation 4 CLFV in +→e+g and -N→e-N Model m k independent L 2 R eL F 2 Lg eL MassqLg qL effective (k 1) (k 1) scalesqu,d probed CLFV Lagrangian ~10,000 times that probed directly by LHC k << 1 k >> 1 magnetic moment type four-fermion interaction operator N → eN >> → eg rate → eg rate ~300X N → eN rate E. Craig Dukes Tau2010 / Mu2e: Lepton Flavor Violation 5 CLFV Sensitive to Many Sources of New Physics Supersymmetry Compositeness Predictions at 10-13 c 3000 TeV Heavy Neutrinos Second Higgs doublet 2 U * U 81013 4 N eN gH e 10 gH Leptoquarks Heavy Z’ Anomalous Z coupling 2 MZ ' 3000 TeV / c 2 17 M L 3000 d ed TeV/c @ B(Z e)10 New physics probed by N→eN (Marciano) E. Craig Dukes Tau2010 / Mu2e: Lepton Flavor Violation 6 E. CraigE. Dukes SUSY GUT w Seesaw Littlest Higgs w T-parity A Few Model Examples Tau2010 / Mu2e: Tau2010 / Mu2e: Violation Flavor Lepton Randall-Sundrum 7 If CLFV Seen: Where is it Coming From? Need: 1. observation of CLFV in more than one Huge number of models channel, and/or predict CLFV: which is it? 2.evidence from LHC, g-2, or elsewhere to allow discrimination between different models MSSM w mSUGRA bc CMSSM-seesaw Yaguma, 2006 Antusch, Arganda, Herrero, Teixeira, 2006 E. Craig Dukes Tau2010 / Mu2e: Lepton Flavor Violation 8 How to Search for -N→e-N • Stop muon in atom -16 ( Al e Al ) • Muon rapidly (10 s) cascades to 1S R state e ( Al Mg) • Circles the nucleus for up to ~2 s • Two things most likely happen: Measure ratio of 1. muon is captured by the nucleus: conversion rate to capture - rate NA,Z→NA,Z-1 2. muon decays in orbit: - - NA,Z→e eNA,Z • In -N→e-N the muon coherently interacts with nucleus leaving it in ground state • signature single isolated electron • Ee = m – ENR - Eb ~ 104.97 MeV (Al) E. Craig Dukes Tau2010 / Mu2e: Lepton Flavor Violation 9 Bunched Beam Technique Needed Need ~1018 stopped muons • Rate too high for continuous beam: need bunched muon beam: 50x109 /s • Need turn off detector for ~ tN Signal: 105 MeV electron coming (~700 ns) while bad stuff (pions, from the target, ~1 s after electrons) is around the is stopped in the foils • Need < 10-9 interbunch contamination bunched beam arrives with ’s, p’s, and electrons Resonant Dipole Extinction aabout huge amount50% of ofthe stuffmuons comes stop inoff the targettarget from scatters, captures etc. need to be sure it isn’t a scatteredlook for a electron delayed or p capture105 MeV electron electron E. Craig Dukes Tau2010 / Mu2e: Lepton Flavor Violation 10 Producing ~1018 Bunched Muons new detector hall and beamline • Energy: 8 GeV Booster beam optimal • Structure: need bunch spacing on order of muon lifetime ~1 s orbit period of Accumulator/Debuncher optimal at 1.7 s • Use Recycler as a transfer line • Stack in Accumulator; bunch in Debuncher • Slow spill extraction: 90% duty factor One of several possible schemes We cannot take any protons away from the Debuncher 12 7 Accumulator 6 batchesFermilab x 4x10 neutrino/1.33 program s x 2x10 s/yr = 3.6x1020 protons/yr Mu2e “steals” 6 of 20 booster batches NOvA cannot use during Main Injector cycle E. Craig Dukes Tau2010 / Mu2e: Lepton Flavor Violation 11 Backgrounds, backgrounds, backgrounds . 1. Stopped Muon Backgrounds Muon decay in orbit (DIO): - - NA,Z→e eNA,Z ▶ defeated by good energy resolution Radiative muon capture (RMC): - + - NA,Z→gNA,Z-1, g→e e ▶ defeated by mZ < mZ-1 ▶ defeated by good energy resolution Muon capture: - NA,Z→N’A’,Z’ + 2n + 0.1p + 2g ▶ defeated by proton absorber 5 E~(E-E0) E. Craig Dukes Tau2010 / Mu2e: Lepton Flavor Violation 12 Backgrounds, Backgrounds, Backgrounds . 2. Prompt Beam Related Backgrounds Radiative pion capture (RPC): - + - p NA,Z→gNA,Z-1 , g→e e Note: 1.2% have Eg > 105 MeV Muon decay in flight: → e Note: p > 77MeV/c Pion decay in flight: p → e e Beam electrons scattering in target ▶ Defeated by 10-9interbunch extinction ▶ Defeated by hard cuts on momentum Antiprotons annihilating ▶ Defeated by thin absorber 3. Time Dependent Backgrounds Cosmic Rays ▶ Defeated by active shield E. Craig Dukes Tau2010 / Mu2e: Lepton Flavor Violation 13 Mu2e Spectrometer Salient Features •Graded solenoidal field for pion capture •Muon transport in curved solenoid to eliminate neutral and positive particles •Pulsed beam to eliminate prompt backgrounds p tgt p 's X p 85,000Look for 100stop MeV every electron 1.7 s 8 GeV/cspiraling50 Booster billion through beamstops/second buncheddetector in Accumulator/Debuncher E. Craig Dukes Tau2010 / Mu2e: Lepton Flavor Violation 14 Transport Solenoidal Magnet • Curved solenoid: 1. separates charges by charge sign 2. reduces line-of-sight transport of neutrals • Collimators eliminate wrong-sign particles, slow late arriving particles, particles with too large momentum E. Craig Dukes Tau2010 / Mu2e: Lepton Flavor Violation 15 Mu2e Detector Salient Features •No detector element in region of transported beam •Small acceptance for DIO electrons •Minimal amount of material detector elements in vacuum Beam dump Electromagnetic Straw tracker Stopping target calorimeter 1T Proton 2T absorber E. Craig Dukes Tau2010 / Mu2e: Lepton Flavor Violation 16 Heart of the Spectrometer: Straw Tracker • Octagonal vane geometry optimized for reconstruction of 105MeV helical trajectories • Center beam region empty Trajectories P > 90MeV • Acceptance for DIO tracks < 10-3 t • Must operate in rates up Low Energy to 200 kHz in individual Target FoilsDIO DIOTrajectories Tail detector elements > 57MeV • Must operate in vacuum: < 10-3 Torr R=57MeV 38 cm • 50% geometrical acceptance: 90°±30° • 0.2 MeV intrinsic energy resolution • Straw tubes: 2,800, 5 mm diam., 2.6 m long, 25m thick • Cathode strips: 17,000 E. Craig Dukes Tau2010 / Mu2e: Lepton Flavor Violation 17 What we Get Intrinsic tracker Perfect Detector energy resolution: Binding + recoil energy DIO tail M (E) 150 keV Average energy loss due to spectrometer material: Real Detector E(shift) 1 MeV M DIO tail E. Craig Dukes Tau2010 / Mu2e: Lepton Flavor Violation 18 Mu2e Sensitivity Proton flux 1.8x1013 p/s (N eN) 7 R Running time 2x10 s e (N N ) Total protons 3.6x1020 p stops/incident proton 0.0025 N e / Ns 1/ e capture probability 0.61 Time window fraction 0.49 v / tot ( 0.609) Electron trigger eff. 0.80 Reconstruction and selection eff. 0.19 -17 Figure of Merit: S/√B = 5.5 Sensitivity (90% CL) 6x10 -16 Detected events for Re = 10 4 -16 for Re = 1 x 10 Estimated background events 0.4 E. Craig Dukes Tau2010 / Mu2e: Lepton Flavor Violation 19 Mu2e Collaboration Boston University R. Carey, K. Lynch, J. Miller*, B. Roberts Brookhaven National Laboratory W. Marciano, Y. Semertzidis, P. Yamin Currently: University of California, Berkeley Yu.G. Kolomensky, T. Ma 117 scientists University of California, Irvine W. Molzon City University of New York J. Popp 23 institutions C. Ankenbrandt , R. Bernstein*, D. Bogert, S. Brice, D. Broemmelsiek, R. Coleman, M. Crisler, D. DeJongh, N. Evans, S. Geer, D. Glenzinski, J. Jackson, D. Johnson, J. Fermi National Accelerator Johnstone, K. Krempetz, R. Kutschke, M. Lamm, M. Martens, M. McAteer, A. Mukherjee, Laboratory S. Nagaitsev, D. Neuffer, A. Norman, R. Ostojic, C. Polly, M. Popovic, E. Prebys, R. Ray, V. Russo, P. Shanahan, M. Syphers, R. Tschirhart, S. Werkema, H. White, K. Yonehara, INFN Lecce F. Grancagnolo, S. Indennidate, A. Mazzacane, M. Peccarisi, G. Tassielli University of Illinois P. Debevec, G. Gollin Institute for Nuclear Research, Moscow V. Lobashev, R. Djilkibaev JINR, Dubna A. Artikov, I. Budagov, V. Glagolev, A. Simonekno, I. Suslov University of Houston E. Hungerford, K. Lau INFN, Frascati M. Cordelli, S. Giovannella, F. Happacher, M. Martini, S. Miscetti, I. Sarra, G. Venanzoni LBNL D. Brown Los Alamos M. Cooper, T. Ito, X. JIang, R. McCrady, P. Walstrom University of Massachusetts D. Kawall, K. Kumar Muons, Inc.
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