Mu2e: Coherent μ→e Conversion Experiment at

David Brown, LBNL representing the mu2e collaboration Charged Flavor Violation • ν mixing implies Charged Lepton Flavor Violation (CLFV)

• Predicted rate is un-observably small • Any observation of 0-ν μ→e transition would be an unambiguous sign of new physics • similar story for τ→μ, τ→e

David Brown, Lawrence Berkeley National Lab 2 mu2e conversion at FNAL PANIC 2011 CLFV in µ+→e+γ and µ-N→e-N Model independent effective CLFV Lagrangian

Loops ‘Contact’ Interactions

κ << 1 κ >> 1 µ → eγ rate ~100X µN → eN >> µN → eN rate µ → eγ rate

David Brown, Lawrence Berkeley National Lab 3 mu2e conversion at FNAL PANIC 2011 Possible Sources of μ→e

Marciano, Mori, and Roney , Ann. Rev. Nucl. Sci. 58 N N - - e e

γ → → -

e

N N - - → µ µ

- µ and accessible by accessible by

Many models predict detectable signals for Λ >> 1 TeV

David Brown, Lawrence Berkeley National Lab 4 mu2e conversion at FNAL PANIC 2011 μ→e Conversion • μ- + N form muonic atom µ-N → e-N μ- tightly bound in K shell • ~20 fm • significant WF overlap with N μ- e- ~4 fm • μ- converts coherently with N • e- recoil is against N • N WF can participate in process • Unique Experimental Signature - • isolated, mono-energetic e with Pe ≅ mμ

David Brown, Lawrence Berkeley National Lab 5 mu2e conversion at FNAL PANIC 2011 Status of CLFV Searches

MEG arXiv:1012.2110

David Brown, Lawrence Berkeley National Lab 6 mu2e conversion at FNAL PANIC 2011 The Mu2e Experiment • Experimental Goal: Measure the ratio Rμe

-17 • 90% C.L. sensitivity to Rμe > 6×10 • 4 orders of magnitude better than current limits • Requires ~ 1018 stopped • ~ 4×1020 protons on target (2 year run @ 25 KW) • Requires negligible (<1) background events • Many challenges for beamline and detector design

David Brown, Lawrence Berkeley National Lab 7 mu2e conversion at FNAL PANIC 2011 Best Previous Measurement SINDRUM-II Prompt Background ❚ Prompt Beam π + N → N*→ N + γ ❚ Cosmic γ + N → N + e+e- Induced ❚ µ Decay

-13 Rμ(Ti) < 6.1X10 David Brown, Lawrence Berkeley National Lab 8 mu2e conversion at FNAL PANIC 2011 The Mu2e Collaboration

Boston University Brookhaven National Laboratory University of California, Berkeley University of California, Irvine California Institute of Technology City University of New York Duke University Fermilab University of Houston University of Illinois, Urbana-Champaign Institute for Nuclear Research, Moscow, Russia JINR, Dubna, Russia INFN Lecce, Università del Salento, Italy Lawrence Berkeley National Laboratory Rice University Los Alamos National Laboratory Syracuse University Northern Illinois University/Lewis University of Virginia Northwestern University College of William and Mary INFN Frascati University of Washington, Seattle INFN Pisa, Università di Pisa, Pisa, Italy ~120 collaborators

David Brown, Lawrence Berkeley National Lab 9 mu2e conversion at FNAL PANIC 2011 Mu2e at FNAL

Mu2e Building

New transfer line

Conditioning in Protons Accumulator and from Booster Debuncher

No intereference with NOVA

David Brown, Lawrence Berkeley National Lab 10 mu2e conversion at FNAL PANIC 2011 Mu2e Apparatus Proton Beam

2.0 T 2.5 T

5.0 T 1.0 T stopping Texttarget ~ 20 meters • Proton delivery beamline • SC solenoids for collection, transportation, and analysis • Primary (proton) and secondary (muon) targets • Active devices: tracker, calorimeter, Cosmic Ray veto

David Brown, Lawrence Berkeley National Lab 11 mu2e conversion at FNAL PANIC 2011 Muon () production

Heavy W, Cu shielding protects SC coil

8 GeV Protons delivered off- axis to Au target

Graded field reflects and focuses low-Pz particles

David Brown, Lawrence Berkeley National Lab 12 mu2e conversion at FNAL PANIC 2011 Momentum Selection ʻSʼ bend transports charged particles, blocks line-of-sight neutrals

muons →

ʻDʼ Collimators select low-momentum negative particles David Brown, Lawrence Berkeley National Lab 13 mu2e conversion at FNAL PANIC 2011 Muon Stopping and Decay Low Pz e- reflected by graded field Muons stop in thin- film Al (Ti) targets e- energy measured in crystal calorimeter

e- momentum measured by straw tracker (in )

David Brown, Lawrence Berkeley National Lab 14 mu2e conversion at FNAL PANIC 2011 Achieving 10-17 Sensitivity • Reduce prompt beam backgrounds • Pulsed beam with < 10-10 inter-pulse rates • ʻSʼ bend transport away from proton target • Veto cosmic rays • Shielding • Active veto with ϵ > 99.99% • Minimize signal window • Precision low-mass tracker • σP/P ~ 10-3

David Brown, Lawrence Berkeley National Lab 15 mu2e conversion at FNAL PANIC 2011 Beam Timing

Inter-bunch protons < 10-10 Muon stopping time

~900 nsec • Prompt decay rapidly • τ = 26 nsec • Muons survive to reach the stopping target • Stopped muon lifetime on Al ~800 nsec David Brown, Lawrence Berkeley National Lab 16 mu2e conversion at FNAL PANIC 2011 e- Momentum Measurement

Tracker has acceptance only for high-P

David Brown, Lawrence Berkeley National Lab 17 mu2e conversion at FNAL PANIC 2011 Momentum Sensitivity

Decay in orbit

Long tail due to nuclear recoil Conversion

Signal Window

Shanker, Phys.Rev D25, 1847 New calculation by Czarnecki etal (1982) agrees within 30% arXiv:1106.4756v1 David Brown, Lawrence Berkeley National Lab 18 mu2e conversion at FNAL PANIC 2011 Backgrounds for 2×107 s Running

Source Events Comment Anti-proton capture 0.06 ± 0.06 Radiative π- capture 0.04 ± 0.02 Assumes 10-10 extinction Beam electrons 0.001 ± 0.001 μ decay in orbit 0.03 ± 0.01 From μ captured on Al Cosmic ray induced 0.025 ± 0.025 Assumes 10-4 inefficiency μ decay in flight 0.01 ± 0.005 With e- scatter in target Total 0.17 ± 0.12

-17 Rμ = 6 × 10 gives ~ 3 events

David Brown, Lawrence Berkeley National Lab 19 mu2e conversion at FNAL PANIC 2011 Mu2e Project Status Mu2e received mission-need approval (CD0) • from DOE in November 2009

Detector Design Solenoid Design Solenoid Fabrication

Detector Hall Construction Detector Construction

David Brown, Lawrence Berkeley National Lab 20 mu2e conversion at FNAL PANIC 2011 Conclusions • CLFV provides a complementary way to search for New Physics compared to LHC • Sensitive to mass scales >> 1TeV • Mu2e is a proposed experiment to search for CLFV muon decays • A unique design provides high sensitivity • 104 improvement relative to previous searches • Mu2e has preliminary FNAL and DOE approval • Conceptual design (almost) complete • Major component fabrication to begin in 2013 • First data in 2018 David Brown, Lawrence Berkeley National Lab 21 mu2e conversion at FNAL PANIC 2011 Backup

David Brown, Lawrence Berkeley National Lab 22 mu2e conversion at FNAL PANIC 2011 Constraints on new physics

David Brown, Lawrence Berkeley National Lab 23 mu2e conversion at FNAL PANIC 2011 Constraints on new physics L. Calibbi, A. Faccia, A. Masiero, S. Vempati hep-ph/0605139

Neutrino-Matrix Like (PMNS) Minimal Flavor Violation (CKM)

Current limits Can distinguish between PMNS and MFV Mu2e

Complementarity between Lepton Flavor Violation (LFV) and LHC experiments

David Brown, Lawrence Berkeley National Lab 24 mu2e conversion at FNAL PANIC 2011 CLFV and Tau Decays τ processes suppressed, but less than µ

Smaler hep-ph/9810484 GIM -40 Cancellations -14 SM ~ 10 because of SM ~ 10 Phys.Rev.D16:1444,1977 Lee, Shrock Shrock Lee, large τ mass Good News: Bad News: Pham, Beyond SM rates are τ’s hard to produce: several orders of ~1010 τ/yr vs ~1011 µ/sec magnitude larger than in fixed-target in associated muon experiments (Mu2e/ decays COMET) 33 25 also e→τ at electron-ion collider? M. Gonderinger, M. Ramsey-Musolf, arXiv:1006.5063v1 David Brown, Lawrence Berkeley National Lab mu2e conversion at FNAL PANIC 2011 Extinction

momentum scrapeing when beam is ‘wide’ |dE/E| = xmax/D

David Brown, Lawrence Berkeley National Lab 4426 mu2e conversion at FNAL PANIC 2011 Mu2e and Project X • Project X: high intensity proton source to replace existing Booster. • Booster: 20 kW beam power at 8 GeV. • Project X: 200 kW at 8 GeV (with upgrade path to 2000 kW). • Sensitivity of Rμe < 10-18 Requires detector, beamline • upgrades

David Brown, Lawrence Berkeley National Lab 27 mu2e conversion at FNAL PANIC 2011 Choice of Stopping Material

rate normalized to Al • Physics reach sensitive to target Z • μ- lifetime, e- momentum also affected

Kitano, et al., PRD 66, 096002 (2002) Z

David Brown, Lawrence Berkeley National Lab 4128 mu2e conversion at FNAL PANIC 2011