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

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

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

BEACH 2010 Mu Measuring couplings of SUSY observed at the LHC. Now Mu 2e

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

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

BEACH 2010 The Measurement Method Stop negative muons in an aluminum foil target The stopped muons quickly form muonic atoms ühydrogenic 1S level around the aluminum nucleus üBohr radius ~20 fm (inside all electrons), Binding E~500 keV üNuclear 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  sec in vacuum Look for a mono-energetic electron from the neutrinoless conversion of a muon to an electron. 8

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

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

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

BEACH MECO spectrometer design for every incident proton   ’s are stopped in the mm Al target foils

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

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 Beam 1.2T 1.0T Graded Field for Magnetic Mirror Effect 1T Solenoidal Field e e Helical Radius J. Miller

BEACH 2010 Octagonal+Vanes geometry is optimized for reconstruction of 105MeV helical trajectories Extremely low mass Acceptance for DIO tracks < R=57MeV Low Energy DIO Trajectories Target Foils DIO Tail > 57MeV Trajectories P t > 90MeV Barrel Vane Electron track J. Miller

BEACH 2010 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 Rates start at 6 MHz/wire but ≲ 180 kHz/wire in live time window Each muon capture produces 2γ, 2n, 0.1p

BEACH The Bottom Line Roughly half of background is beam related, and half interbunch contamination related Total background per 4x10 20 protons, 2x10 7 s:0.43 events Signal for R  e = :5 events Single even sensitivity: 2x % C.L. upper limit if no signal:6x Blue text: beam related.

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

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

BEACH 2010 Summary The Mu2e collaboration has embarked on an search for coherent muon to electron conversion that is x10 4 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 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 2.5 T 2.1 T

BEACH 2010 Tracking Detector/Calorimeter m straws  (r,  ) ~ 0.2 mm Cathode strips  z) ~ 1.5 mm 1200 PbOW 4 crystals in the electron calorimeter  E/E ~ 3.5% Resolution:.19 MeV/c 23

BEACH A long time coming 1992MELC proposed at Moscow Meson Factory 1997 MECO proposed for the AGS at Brookhaven as part of RSVP (at this time, experiment incompatible with Fermilab) intensive work on MECO technical design: magnet system costed at $58M, detector at $27M July 2005RSVP cancelled for financial reasons 2006 MECO subgroup + Fermilab physicists work out means to mount experiment at Fermilab June 2007mu2e EOI submitted to Fermilab October 2007LOI submitted to Fermilab Fall 2008mu2e submits proposal to Fermilab, Granted Stage-I Approval! 2010technical design approval: start of construction 2014first beam

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

BEACH 2010 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 (E s -E) 5 Drives resolution requirement. 26 N Ordinary: Coherent: