Search for Coherent Muon to Electron Conversion: The Mu2e experiment at Fermilab

1. Search for Coherent Muon to Electron Conversion:The Mu2e experiment at Fermilab R. Tschirhart Fermilab BEACH 2010, Perugia Italy

2. Forbidden in Standard Model Observation of neutrino mixing shows this can occur at a very small rate Photon can be real (m->eg) or virtual (mN->eN) The deepest probe of Lepton Flavor Physics: Ultra-rare m-Decays: First Order FCNC: Higher order dipole “penguin”: Virtual n mixing The MEG(PSI) experiment has probed to 10-11 level. 2 BEACH 2010

3. Rare muon decays in Project-X:m-N→e-N Sensitivity to New Physics Supersymmetry Compositeness Predictions at 10-15 Second Higgs doublet Heavy Neutrinos Heavy Z’, Anomalous Z coupling Leptoquarks After W. Marciano BEACH 2010

4. Measuring couplings of SUSY observed at the LHC. Now Mu2e Mu2e@Project-X BEACH 2010

5. Rare t: Measuring couplings of SUSY observed at the LHC. BEACH 2010

6. The Mu2e Collaboration • Boston University, USA. • Brookhaven National Laboratory, USA. • City University of New York, USA. • College of William and Mary, USA. • Fermi National Accelerator Laboratory, USA. • INFN-Lecce, Italy. • INFN-Pisa, Italy • Institute for Nuclear Research, Russia. • JINR (Dubna), Russia. • Laboratori Nazionale Di Frascati, Italy. • Los Alamos National Laboratory. • Muons Inc, USA. • Northwestern University, USA. • Rice University, USA. • Syracuse University, USA. • University of California-Berkeley, USA. • Lawrence Berkeley National Laboratory, USA. • University of Houston, USA. • University of Illinois, Urbana, USA. • University of California-Irvine, USA. • University of Massachusetts-Amherst, USA. • University of Virginia, USA. • 3 Countries, 22 institutes • 4 US National Laboratories • 1 Italian National Laboratory Funding Agencies (DOE) “The Mu2e Experiment should be pursued under all funding scenarios…” BEACH 2010

7. Low E Muons Collider Muons Our muons are not like your muons... In these “stopped” muon experiments muons are highly ionizing particles and electrons are minimum ionizing particles! BEACH 2010

8. The Measurement Method 8 BEACH 2010 • Stop negative muons in an aluminum foil target • The stopped muons quickly form muonic atoms • hydrogenic 1S level around the aluminum nucleus • Bohr radius ~20 fm (inside all electrons), Binding E~500 keV • Nuclear radius ~ 4 fm  muon and nuclear wavefunctions overlap • Muon lifetime in 1S orbit of aluminum ~864 ns (40% decay, 60% nuclear capture), compared to 2.2 msec in vacuum • Look for a mono-energetic electron from the neutrinoless conversion of a muon to an electron.

9. Coherent conversion kinematics Starting with a muonic atom in the 1s state... ...then conversion happens... ... a 1-to-2 process producing monochromatic electrons! 20 fm BEACH 2010

10. Previous muon decay/conversion limits (90% C.L.) Rate limited by need to veto prompt backgrounds! m->e Conversion: Sindrum II LFV m Decay: High energy tail of coherent Decay-in-orbit (DIO) Eur. Phys. J. C 47, 337–346 (2006) 10 BEACH 2010

11. DC Beam What Limited SINDRUM-II? no time separation between signal and prompt background radiative π capture cosmic rays also an issue; need excellent veto, ~99.9% BEACH 2010

12. mu2e Muon Beam and Detector for every incident proton 0.0025 m-’s are stopped in the 17 0.2 mm Al target foils MECO spectrometer design 12 BEACH 2010

13. Proton bunch Pions and muons arrive at target Detector live window Prompt: Radiative Pion Capture with pair production Delayed: Muon Decay-in-Orbit The two most dangerous backgrounds have very different timing properties. The FNAL accelerator complex produces proton beams with a pulsed structure. 1.7 msec BEACH 2010

14. The Detector Graded Field forMagnetic Mirror Effect Helical Radius 1.0T e Beam 1T Solenoidal Field 1.2T J. Miller BEACH 2010 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

15. Straw Tracker (In Vacuum) Vane Trajectories Pt > 90MeV Barrel Electron track Low Energy DIO Trajectories DIO Tail > 57MeV Target Foils R=57MeV J. Miller BEACH 2010 Octagonal+Vanes geometry is optimized for reconstruction of 105MeV helical trajectories Extremely low mass Acceptance for DIO tracks < 10-13

16. Magnetic Spectrometer:Rates vs. Time • Rates start at 6 MHz/wire but • ≲ 180 kHz/wire in live time window • Each muon capture produces 2γ, 2n, 0.1p BEACH 2010

17. The Bottom Line Blue text: beam related. Roughly half of background is beam related, and half interbunch contamination related Total background per 4x1020 protons, 2x107 s: 0.43 events Signal for Rme = 10-16: 5 eventsSingle even sensitivity: 2x10-1790% C.L. upper limit if no signal: 6x10-17 17 BEACH 2010

18. Cost and Schedule • This is a technically limited schedule • Critical Path is Superconducting Solenoids • $200M “fully-loaded” Total Cost data-taking 1st quarter Calendar 2016 BEACH 2010

19. US Gov’t DOE CD Process Experimenter’s Reward Lasciate ogne speranza, voi ch’intrate Inferno fresco in Camposanto, Pisa CD process BEACH 2010

20. Guide to DOE CD Process • CD–0: “mission need” • the DOE decides this is part of its goals and then DOE prepares document • DOE: Feb 2009 for Mu2e • CD–1: “conceptual design” • careful, systematic evaluation of alternatives • cost and schedule well along but not final • CD–2: “baseline” / technical design • firm cost and schedule estimates for entire experiment • CD–3: Build Experiment! BEACH 2010

21. Summary • The Mu2e collaboration has embarked on an search for coherent muon to electron conversion that is x104 more sensitive that previous searches, and sensitive to many TeV-scale extensions of the Standard Model. • The technique is driven with an intense pulsed muon source of exceptional purity delivered with a set of novel super-conducting solenoids. • The detector must tag and measure the momenta of 100 MeV conversion electrons with very high precision. • The collaboration is continuing to grow, and there are opportunities to participate in this pursuit of physics beyond the Standard Model. BEACH 2010

22. Transport Solenoid • Curved solenoid eliminates line-of-sight transport of photons and neutrons • Curvature drift and collimators sign and momentum select beam • dB/ds < 0 in the straight sections to avoid trapping which would result in long transit times Collimators and pBar Window 2.1 T 2.5 T 22 BEACH 2010

23. Tracking Detector/Calorimeter 3000 2.6 m straws s(r,f) ~ 0.2 mm 17000 Cathode strips s(z) ~ 1.5 mm 1200 PbOW4 crystals in the electron calorimeter sE/E ~ 3.5% Resolution: .19 MeV/c 23 BEACH 2010

24. A long time coming 24 BEACH 2010

25. Magnetic Field Gradient Production Solenoid Transport Solenoid Detector Solenoid 25 BEACH 2010

26. Decay in Orbit (DIO) Backgrounds: Biggest Issue Very high rate Peak energy 52 MeV Must design detector to be very insensitive to these. Nucleus coherently balances momentum Rate approaches conversion (endpoint) energy as (Es-E)5 Drives resolution requirement. Ordinary: Coherent: N 26 BEACH 2010