1 / 77

Mu2e: A New Search for Charged Lepton Flavor Violation at Fermilab

Mu2e: A New Search for Charged Lepton Flavor Violation at Fermilab. Jim Miller Boston University for the Mu2e Collaboration 26 June 2009. Outline. Brief introduction and theoretical motivation Description of main backgrounds, experimental technique and proposed apparatus

sivan
Download Presentation

Mu2e: A New Search for Charged Lepton Flavor Violation at Fermilab

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Mu2e: A New Search for Charged Lepton Flavor Violation at Fermilab Jim Miller Boston University for the Mu2e Collaboration 26 June 2009 J. Miller, BU PAVI 09 June, 2009

  2. Outline • Brief introduction and theoretical motivation • Description of main backgrounds, experimental technique and proposed apparatus • Description of Fermilab Accelerator • Potential Future Upgrades • Conclusions J. Miller, BU PAVI 09 June, 2009

  3. What is μe Conversion? • Charged Lepton Flavor Violation (CLFV) • Related Processes: • μeγ, τeγ, τmγ, μe+e-e , te+e-e , t m+m-m A muon converts to an electron in the presence of a nucleus, with no neutrinos. The nucleus is required to conserve energy and momentum! J. Miller, BU PAVI 09 June, 2009

  4. Muon to Electron Conversion x10000 improvement over current limit J. Miller, BU PAVI 09 June, 2009

  5. e- Experimental Signal • A Single Monoenergetic Electron • ForAluminum, Ee = 105 MeV • electron energy depends somewhat on Z Ee=mmc2-BE-Recoil J. Miller, BU PAVI 09 June, 2009

  6. Endorsed in US Roadmap A muon-electron conversion program at FNAL: Strongly endorsed by P5 “The experiment could go forward in the next decade with a modest evolution of the Fermilab accelerator complex. Such an experiment could be the first step in a world-leading muon-decay program eventually driven by a next-generation high-intensity proton source. The panel recommends pursuing the muon-to-electron conversion experiment... under all budget scenarios considered by the panel” Mu2e is a central part of the future US program Mu2e received Stage I approval from the FNAL PAC and Directorate in November, 2008. J. Miller, BU PAVI 09 June, 2009

  7. Collaboration • Boston University: R.M. Carey, K.R. Lynch, J.P. Miller*, B.L. Roberts • BNL:W. Marciano,Y. Semertzidis, P. Yamin • UC Berkeley: Yu.G. Kolomensky • FNAL:C.M. Ankenbrandt , R.H. Bernstein*, D. Bogert, S.J. Brice, D.R. Broemmelsiek, R. Coleman, D.F. DeJongh, S. Geer, D. Glenzinski ,R. Kutschke, M. Lamm, , P.J. Limon, M.A. Martens, S. Nagaitsev, D.V. Neuffer, M. Popovic, E.J. Prebys, V. Rusu , P. Shanahan, M. Syphers, R.E. Ray, R. Tschirhart, H.B. White, K. Yonehara, C.Y. Yoshikawa • Idaho State University: D. Dale, K.J. Keeter, E. Tatar • UC Irvine: W. Molzon • University of Illinois/Champaign-Urbana: P.T. Debevec, G. Gollin,D.W. Hertzog, P. Kammel • INFN/Università Di Pisa:F. Cervelli, R. Carosi, M. Incagli,T. Lomtadze, L. Ristori, F. Scuri, C. Vannini • INR Moscow: V. Lobashev • U Mass Amherst: D. Kawall, K. Kumar • Muons, Inc: R.J. Abrams, M.A.C. Cummings, R.P. Johnson, S.A. Kahn,S.A. Korenev, T.J. Roberts, R.C. Sah • City University of New York:J.L. Popp • Northwestern University:A. DeGouvea • Rice University: M. Corcoran • Syracuse University: R.S. Holmes, P.A. Souder • University of Virginia: M.A. Bychkov, E.C. Dukes, E. Frlez, R.J. Hirosky, A.J. Norman, K.D. Paschke, D. Pocanic 70 Collaborators 16 Institutions J. Miller, BU PAVI 09 June, 2009

  8. History of CLFV Searches J. Miller, BU PAVI 09 June, 2009

  9. Lepton Flavor Violation Searches Current and Planned Expts • Neutrino Oscillations! • t decays at Babar, Belle. • Future t decays: Super B factories • MEG at PSI: μ→eγ • me conversion: • Mu2e at FNAL • COMET at JPARC L. Calibbi, A. Faccia, A. Masiero, S. Vempati hep-ph/0605139 BR(me in Au) <7x10-13 BR(tl+l-l) <(few)x10-8 BR(tmg) <4.2x10-8 J. Miller, BU PAVI 09 June, 2009

  10. Neutrino Oscillations and me • n’s have mass! Individual lepton numbers are not conserved • This implies lepton flavor violation also occurs in charged • leptons. In the SM (extended to handle neutrino oscillations): • SM: Branching ratio(mNeN)<10-52 • This is way below any experimental sensitivity • Other CLFV reactions are similarly suppressed • Any observation of CLFV is a definite sign of new physics • Many models predict CLFV at levels just beyond current limits J. Miller, BU PAVI 09 June, 2009

  11. New Physics Contributions to μe Conversion From W. Marciano. also see Flavour physics of leptons and dipole moments, arXiv:0801.1826 J. Miller, BU PAVI 09 June, 2009

  12. Power of Signal in Muon-Electron Conversion BR(me) vs M1/2 for tanb=10 Neutrino-Matrix Like (PMNS) Minimal Flavor Violation(CKM) BR(me)x1012 Current me limit Proposed me limit M1/2(GeV) L. Calibbi, A. Faccia, A. Masiero, S. Vempati hep-ph/0605139 neutrino mass via the see--saw mechanism,analysis in SO(10) framework J. Miller, BU PAVI 09 June, 2009

  13. Similar Plots for tmgand meg BR(tmg) x107 vs M1/2 for tanb=10 L. Calibbi, A. Faccia, A. Masiero, S. Vempati hep-ph/0605139: neutrino mass via the see--saw mechanism,analysis in SO(10) framework BR(meg) x1011vs M1/2 for tanb=10 J. Miller, BU PAVI 09 June, 2009

  14. Mu2e MEG μ→e Conversion versus μ→eγ MEG Little Higgs Model w/T parity M. Blanke, A. J. Buras, B. Duling, A. Poschenrieder and C. Tarantino, JHEP 0705, 013 (2007). Mu2e BR(mTieTi) BR(meg) Constrained Minimal SUSY SO(10) models C. Albright and M. Chen, arXiv:0802.4228, PRD D77:113010, 2008. MEGA J. Miller, BU PAVI 09 June, 2009

  15. SUSY: Minimal SU(5) m>0 m<0 J. Hisano, T. Moroi, K. Tobe and M. Yamaguchi, Phys. Lett. B 391, 341 (1997). [Erratum-ibid. B397, 357 (1997).] J. Miller, BU PAVI 09 June, 2009

  16. Sensitivity of Mu2e Single-event sensitivity= 2.5 x 10-17 Rμe < 6 x 10-17 90% CL • For Rμe = 10-15 • ~40 events / 0.4 bkg (LHC SUSY?) • For Rμe = 10-16 • ~4 events / 0.4 bkg J. Miller, BU PAVI 09 June, 2009

  17. Outline • Brief introduction and theoretical motivation • Description of main backgrounds, experimental technique and proposed apparatus • Description of Fermilab Accelerator • Potential Future Upgrades • Conclusions J. Miller, BU PAVI 09 June, 2009

  18. The Measurement Method in a Nutshell • Stop negative muons in an aluminum target • The stopped muons form muonic atoms • hydrogenic 1S level in aluminum nucleus • Bohr radius ~20 fm, Binding E~500 keV • Nuclear radius ~ 4 fm muon and nuclear wavefunctions overlap • Muon lifetime in 1S orbit of aluminum ~864 ns compared to 2.2 msec in vacuum 40% decay, 60% nuclear capture, (capture is ~ sum of reactions over protons in nucleus) • Look for a monoenenergetic electron from the neutrinoless conversion of a muon to an electron, leaving the nucleus in the ground state: • Measured quantity: the ratio Rme: J. Miller, BU PAVI 09 June, 2009

  19. Backgrounds from Stopped Muons: Muon Decay in Atomic Orbit (DIO) Decay in Orbit electrons Simulation (Assume Rme~10-16) m-e- FWHM~0.9 MeV, s ~ 0.3 MeV on high side tail Conversion electrons of interest: [m- + Al(13,27)]bound -> Al(13,27) + e- (105 MeV) Electrons from decay of bound muons (DIO) -- kinematic endpoint equals conversion electron energy: J. Miller, BU PAVI 09 June, 2009

  20. Backgrounds from Stopped Muons(Cont’d) • Ordinary muon capture on the nucleus • In neutron capture, secondary particles can be produced • n, p are low energy, g are mostly low energy, well below conversion electron energy: create high rate background in detectors, potential track recognition errors • Neutral background (n, g) is reduced by displacing detectors downstream from the stopping target • Protons are reduced by placing thin absorbers in their path • Radiative Muon Capture, g energy above 55 MeV, prob ~ few x 10-5; endpoint for aluminum 102.4 MeV, 2.5 MeV below conversion electron energy. Event rate comparable to DIO at 102.5 MeV, rises much slower than DIO at lower energies. J. Miller, BU PAVI 09 June, 2009

  21. Radiative Pion Capture Background • p-, like m-, stop in stopping target and form atoms • Radiative Pion Capture • Reaction of p- with nucleus is fast: occurs part way through atomic cascade • BR 2% for photon > 55 MeV, peak prob ~110 MeV, endpoint~137 MeV • g + material (e.g. target)  e+e- ; e- may have energy > 100 MeV J. Miller, BU PAVI 09 June, 2009

  22. Previous Data, mNeN High energy tail of Decay-in-orbit (DIO) electrons. Simulated conversion peak From SINDRUM Experiment • Rate limited by need to veto prompt backgrounds! pulsed beam DC beam J. Miller, BU PAVI 09 June, 2009

  23. Dealing with radiative pion capture background Simulation Time distribution of pions arriving at target after proton strikes the production target Mu2e plans a pulsed proton beam Well-matched to 864 ns muonic Al lifetime • Wait ~700 ns to start measurement, pion stopping rate is reduced by ~1011 ~0.0007 events background, compared to ~4 events signal at Rme=10-16 • Extinction (=between-pulse proton rate) < 10-9 gives ~0.07 counts • Recognized and studied by time dependence, presence of e+ J. Miller, BU PAVI 09 June, 2009

  24. Mu2e Muon Beamline and Detector Requirements • Pulsed beam- 109 extinction • High fluxm-beam to stopping target • At FNAL, high proton flux ~20x1012 Hz, 8 GeV • Mu2e: use solenoidal muon collection and transfer scheme • muons ~5 x 1010 Hz , 1018 total needed • Muon properties • low momentum and/or narrow momentum spread • stop max # muons in thin target • avoid ~105 MeV e- from in-flight m- decay (keep pm<75 MeV/c) • Background particles from beam line must be minimized • especially ~105 MeV e-and high momentum m- • a major factor driving design of muon beamline • Detector should have high resolution and acceptance for 105 MeV electrons J. Miller, BU PAVI 09 June, 2009

  25. Mu2e Muon Beamline- follows MECO design Muons are collected, transported, and detected in superconducting solenoidal magnets Muon Stopping Target Calorimeter Tracker Proton Beam Muon Beam Collimators Target Shielding Proton Target B=1 T B=1 T Pions Electrons Detector Solenoid B=2 T Muons B=2.5 T Transport Solenoid B=5 T Production Solenoid Delivers 0.0025 stopped muons per 8 GeV proton J. Miller, BU PAVI 09 June, 2009

  26. J. Miller, BU PAVI 09 June, 2009

  27. Production Solenoid Magnetic Mirror Effect 8GeV Incident Proton Flux 3×107 p/pulse (34ns width) 5T Gradient Solenoid Field 2.5T p μ π π Primary πproduction off gold target ¹ π decays to μ μ is captured into the transport solenoid and proceeds to the stopping targets

  28. Transport Solenoid Inner bore radius=25 cm Length=13.11 m Toroid bend radius=2.9 m Curved sections eliminate line of sight transport of n, g. Radial gradients (dBs/dR) in toroidal sections cause particles to drift vertically; off-center collimator signs and momentum selects beam dB/dS < 0 in straight sections to avoid slow transiting particles Collimation designed to greatly suppress transport of e- greater than 100 MeV Length decreases flux, by decay, of pions arriving at stopping target in measurement period B=2.5T B=2.4T Beam particles • Goals: • Transport low energy • m- to the detector solenoid • Minimize transport of positive particles and high energy particles • Minimize transport of neutral particles • Absorb anti-protons in a thin window • Minimize particles with long transit time trajectories B=2.4T B=2.1T B=2.1 T B=2.0 T To stopping target J. Miller, BU PAVI 09 June, 2009

  29. Separation of m-from m+ m- m+ 29 J. Miller, BU PAVI 09 June, 2009

  30. The Detector • The detector is specifically design to look for the helical trajectories of 105 MeV electrons • Each component is optimized to resolve signal from the Decay in Orbit Backgrounds Graded Field forMagnetic Mirror Effect 1T Beam in 1T 2T

  31. Detector Solenoid • Solenoid, 1m radius, B=2 T1T from 0 to 4 m, B=1 T from 4 to 10 m • Negative field gradient at target creates mirror increasing detector acceptance. • Stopping target: thin to reduce loss of energy resolution due to energy straggling Calorimeter Tracker Stopping Target Muon Beam Line B=1T Uniform field B=1T Large flux of electrons from low energy portion of muons decaying in target (DIO) spiral harmlessly through the centers of the detectors Field gradient<0 Muons B=2T J. Miller, BU PAVI 09 June, 2009

  32. Straw Tracker (In Vacuum) • Octagonal+Vanes geometry is optimized for reconstruction of 105MeV helical trajectories • Extremely low mass • Acceptance for DIO tracks < 10-13 Vane Trajectories Pt > 90MeV Barrel Electron track Low Energy DIO Trajectories DIO Tail > 57MeV Target Foils R=57MeV

  33. Calorimeter • Function: provide initial trigger to system (E>80 MeV gives trigger rate ~1 kHz), and redundant position, timing, and energy information • 1800 PbWO4 crystals, 3 x 3 x 12 cm3 arranged in four vanes. Density 8.3g/cm3, Rad. Length 0.89 cm, R(Moliere)=2.3 cm, decay time 25 ns • Each crystal is equipped with two large area Avalanche Photo-Diodes: gives larger light yield and allows identification of events with charged particles traversing photodiode • Both the front end electronics (amplifier/shapers) and the crystals themselves are cooled to -240 C to improve PbWO4 light yield and reduce APD dark current. • Single crystal performance has been demonstrated by MECO with cosmic rays: 38 p.e./MeV, electronic noise 0.7 MeV. Estimated performance with electrons, s~5-6 MeV at 100 MeV, sposition<1.5 cm 33 J. Miller, BU PAVI 09 June, 2009

  34. Cosmic Ray Veto and Shielding • Active shielding goal: inefficiency <10-4 • Simulation study has shown that 10- 4 inefficiency in scintillator veto 0.016 background events / 2x107s. • Three overlapping layers of scintillator consisting of 10 cm x 1 cm x 4.7 m strips. Veto= signals in 2 or more layers. • Cost-efficient MINOS approach: extruded (not cast) scintillator,1.4 mm wavelength-shifting fiber. • Use multi-anode PMT readout of WLS fiber • Passive shielding: heavy concrete plus 0.5 m magnet return steel. Steel also shields CRV scintillator from neutrons coming from the stopping target. J. Miller, BU PAVI 09 June, 2009

  35. Extinction Scheme • Need to achieve (out-of-time flux)/(in-time flux)<10-9 • Sweep protons out of beam between proton pulses: • Continuous Extinction monitoring techniques under study • Telescope to measure secondary proton production as in MECO • Joint effort with COMET to develop in-beam proton veto counter. Under development J. Miller, BU PAVI 09 June, 2009

  36. Background Summary (DIO) * Due to out-of-time protons, depends on extinction, 10-9 assumed (From MECO simulations, in process of being repeated by Mu2e) Total run time, 2x107 seconds Total protons, 4x1020 Total stopped muons, 1x1018 Total conversion electrons (if Rme=10-16)=4 counts J. Miller, BU PAVI 09 June, 2009

  37. Outline • Brief introduction and theoretical motivation • Description of main backgrounds, experimental technique and proposed apparatus • Description of Fermilab Accelerator • Potential Future Upgrades • Conclusions J. Miller, BU PAVI 09 June, 2009

  38. FNAL Beam Delivery • FNAL has unique, major strength: • Multiple Rings • no interference with NOvA neutrino oscillation experiment • reuse existing rings with only minor modifications J. Miller, BU PAVI 09 June, 2009

  39. Mu2E & NOνA/NuMI • How do we deliver O(1018) bunched m’s? Mu2e Detector Hall To NuMI Use NuMI cycles in the Main injector to slow spill to Mu2e. No Impact on NOvA Results in: 6 batches x 4x1012 /1.33 s x 2x107 s/yr = 3.6 x1020protons/yr

  40. “Boomerang Scheme” • Booster Batches transported partway through Recycler and injected directly into Accumulator • Stack batches in Accumulator • Transfer to Debuncher • Rebunch into Single Bunch: • 38 nsec RMS, ±200 MeV • Period~ 1700 ns • Slow resonant extraction: transverse, yields bunch “train”: desired pulsed beam J. Miller, BU PAVI 09 June, 2009

  41. Beam Sharing time to ramp allows us to fit eight extra Booster batches for Mu2e (can use 6) J. Miller, BU PAVI 09 June, 2009

  42. Outline • Brief introduction and theoretical motivation • Description of main backgrounds, experimental technique and proposed apparatus • Description of Fermilab Accelerator • Potential Future Upgrades • Conclusions J. Miller, BU PAVI 09 June, 2009

  43. Experimental Advantage of m e and Upgrade Path • Production of lots of muons is relatively easy • Conversion electron energy, 105 MeV, is far above the bulk of low energy decay electron background. Considerable improvement in the ultimate sensitivity is quite possible. • With additional improvements in detectors, beam line, fluxes, it may be possible to get Rme <10-18 or better. • Contrast with m eg: • Method: look for back-to-back 53 MeV electron and photon • e and g energies are right at the maximum flux of electron energies from ordinary muon decay. There can be a significant rate of accidental coincidence between Michel electrons and photons from other events, or from radiative muon decay. These backgrounds are believed to limit future improvements in achievable limits on the branching ratio. J. Miller, BU PAVI 09 June, 2009

  44. What is Project X? • Project X is a concept for an intense 8 GeV proton source that provides beam for the Fermilab Main Injector and an 8 GeV physics program. • The source consists of an 8 GeV superconducting linac that injects into the Fermilab Recycler J. Miller, BU PAVI 09 June, 2009

  45. available 8 GeV Power for intensity frontier 20 kW (current) 200 kW (Project X) 2000 kW (Project X Upgrades) Mu2e and Project X • First establish a signal or set a strong limit -- what do we do next? • Project X gives us a chance to upgrade the experiment by up to x100 J. Miller, BU PAVI 09 June, 2009

  46. Change Z of Target to determine source of new physics Signal? Upgrade Plans... Yes Yes No 1. Both Prompt and DIO backgrounds must drop to measure Rμe~ 10-18 2. Detector, Muon Transport, Cosmic Ray Veto, Calorimeter J. Miller, BU PAVI 09 June, 2009

  47. Schedule • Received Stage-1 Approval and DOE’s CD-0 anticipated shortly • Technically Driven Schedule (wholly magnet driven) results in 2016 start of data taking • Opportunities for Significant R&D, Test Beam, and Auxiliary Measurement work for students and university groups

  48. Conclusions • Strong physics case for muon to electron conversion: • Lepton flavor conservation properties are at the core of understanding why we have three generations • A positive signal indicates new physics • me can be large in most extensions to the SM • me likely has the greatest potential experimental sensitivity for CLFV • Energy reach can be well beyond forseeable accelerators • Addresses P5 goal of Terascale (and often well beyond) sensitivity to new physics complementary to LHC, and has strong P5 endorsement • Mu2e experiment is based on MECO design • Innovative design to obtain the muon beam • Many successful MECO reviews • Physics • Experimental design and Costing • Exceptional fit at FNAL • Desired beam can be had with modest modifications to existing facilities • Operation with minimal impact on NoVA program • Possibility of x100 improvement with Project X and detector upgrades J. Miller, BU PAVI 09 June, 2009

  49. END J. Miller, BU PAVI 09 June, 2009

  50. Vertical Drift Motion in a Toroid Toroidal Field: Axial field Bs=constant x 1/r. This gives a large dBs/dr Particle spiral drifts vertically (perpendicular to the plane of the toroid bend): D= vertical drift distance pl=longitudinal momentum pt=transverse momentum R=major toroid radius=2.9 m, s/R = total toroid bend angle=900 D[m]=distance, B[T], p[GeV/c] B Toroid B field line R J. Miller, BU PAVI 09 June, 2009

More Related