The Mu2e Experiment.Key

The Mu2e Experiment: Searching for μ→e Conversion

David Brown, LBNL

1 μ- N→e- N Conversion • μ- converts coherently with Nucleus - - • no νµ: e recoils against N 27 μ Al - • Experimental Signature e • isolated, mono-energetic e-

Econversion = 104.973 MeV (for Al) µ • ν P SM rate prediction is < 10-54 ( -oscillation) N • ν γ μ- • Background processes: e̅ - ν μ N(A,Z)→ νμ N(A,Z-1)* (nuclear capture, 61%) - • e μ - - 27 - ν • μ N(A,Z)→ νμ e νē N(A,Z) (Decay In Orbit, 39%) Al μ

David Brown, LBNL 2 The Mu2e Experiment Tau 2014 Mu2e can discover Mu2e can discover

RPV SUSYSUSY RPV SUSY μ→e ConversionSUSY ProcessesSecond Higgs doublet Second Higgs doublet µ µ ˜ µ µ 0 u˜ 0 e µ e e • ‘Loop’ termsµ ˜0 e 0 u˜ 0 0e e e e µ˜ µ˜ • i.e. SUSY, Higgse˜ doublets, ... d e˜ H t d H t • Also mediates μ→eγ q q q q q q q q q q q q • ‘Contact’ terms Leptoquarks Z 0/anomalous couplings Z 0/anomalous couplings • Couples leptons to quarks Leptoquarks Extra dimensions, etc. Extra dimensions, etc. µ e Only µaccessible byq μN→eN µ q µ e • Theory reviews: Effective Lagrangian Theory reviews: • Y. Kuno, Y. Okada, 2001 LQ Z0 Y. Kuno, Y. Okada, 2001 κ = contact/loop LQ M. Raidal et al., 2008Z0 • M. Raidal et al., 2008 q q q A. deGouvea, P. Vogel, 2013 • Λ = mass scale e q q q A. deGouvea, P. Vogel, 2013 Loop Contacte

Andrei Gaponenko 5 PSI2013

David Brown, LBNL 3 Andrei GaponenkoThe Mu2e Experiment Tau 2014 5 PSI2013 μ→e Conversion Physics Reach

W. Altmannshofer, A.J.Buras, S.Gori, P.Paradisi, D.M.Straub = Discovery= Sensitivity arXiv:0909.1333[hep-ph]

Excellent sensitivity to many BSM models

David Brown, LBNL 4 The Mu2e Experiment Tau 2014 Previous Measurements • Sindrum-II SINDRUM-II μTi→eTi (1996) • Backgrounds: • beam π- and e- beam • cosmic muons • DIO

RμeTi < 6.1X10-13 PANIC 96 (C96-05-22) DIO RμeAu < 7X10-13 Eur.Phys.J. C47 (2006) cosmic Mu2e goal: RμeAl < 6X10-17

David Brown, LBNL 5 The Mu2e Experiment Tau 2014 Mu2e Physics Sensitivity

• Mu2e will be sensitive over the full κ range • Exceed current (and future) limits for both Loop and Contact term interactions Courtesy Courtesy B. and Bernstein A. Gouvea de • Mu2e will be sensitive to effective mass scales up to 104 TeV • ~1 order of magnitude improvement over current mass scale limits

Loop Contact dominated dominated David Brown, LBNL 6 The Mu2e Experiment Tau 2014 Mu2e Collaboration

Boston University Brookhaven National Laboratory Lawrence Berkeley National Laboratory University of California, Berkeley University of California, Irvine California Institute of Technology City University of New York Duke University Fermi National Accelerator Laboratory Currently: University of Houston ~140 scientists University of Illinois 28 institutions Lewis University University of Massachusetts, Amherst Laboratori Nazionali di Frascati Muons Inc. INFN Genova Northern Illinois University INFN Lecce and Università del Salento Northwestern University INFN Lecce and Università Marconi Roma Pacific Northwest National Laboratory INFN Pisa Purdue University Universita di Udine and INFN Trieste/Udine Rice University University of Virginia University of Washington Joint Institute for Nuclear Research, Dubna Institute for Nuclear Research, Moscow

David Brown, LBNL 7 The Mu2e Experiment Tau 2014 The Mu2e Experiment

Detector Solenoid ~ 22 Muon m Beam Stop 1T ←2 T

Tracker Stopping Target

Calorimeter

Transport Proton Beamline Solenoid~2 T Production Solenoid 2.5T ← 4.5 T Extinction Monitor Production Target

David Brown, LBNL 8 The Mu2e Experiment Tau 2014 Mu2e Beam Delivery • Protons from 8 GeV booster • Delivered through former Tevatron Anti-Proton complex • Tightly bunched pulses • Resonant Extraction • Active “Extinction” • Out-of-time proton fraction < 10-10 0.08 POT pulse 0.07 - arrival/decay time ( × 1M ) - 0.06 µ arrival time ( × 400 ) π µ- decay/capture time ( × 400 ) 0.05 0.04 μ 0.03 200 Detector Livegate (1μsec) 0.02 nsec 0.01 0 0 200 400 600 800 1000 1200 1400 1600 1800 Time (ns) David Brown, LBNL 9 The Mu2e Experiment Tau 2014 Transport Solenoid • ‘S’ blocks line-of-sight t • Bend induces momentum, charge-dependent vertical shift • Asymmetric collimator μ- rejects positive and high- momentum particles • Can be rotated to select positive particles μ+

V. Lobashev, MELC 1992:

David Brown, LBNL 10 The Mu2e Experiment Tau 2014 Low-Mass Straw Tracker

1.4 m 3 m

• 20 stations of straw chambers 1 station = 12 semi-circular straw panels • DIO Peak • 3-D printed manifolds • 15 μm mylar/Al/Au wall straws - Average mass transited by e ~1% x0 • Conversion • Time division readout (3-D points) • few cm resolution (~100 ps) David Brown, LBNL 11 The Mu2e Experiment Tau 2014 Scintillating Crystal Calorimeter

• Dual Disk design provides >90% acceptance • Hexagonal BaF2 or CsI crystals • SIPM or APD readout • Provides PID (μ background rejection), alternate track seed, alternate trigger David Brown, LBNL 12 The Mu2e Experiment Tau 2014 3-60 Mu2e Technical Design Report Cosmic Rays

• Cosmic muons can scatter or eject e- from detector material Suppression requires an active veto Figure• 3.32 An event display from simulation showing a background candidate induced from a through-going cosmic ray that interacts in the calorimeter to create an electron. The electron, shown• incoverage red, first travels over upstream, detector then gets reflected and and stopping travels downstream target through the tracker. Both the upstream and downstream segments are reconstructed (light blue and dark blue). 4 layers of overlapping scintillation counters About• two-thirds of the surviving events are electrons with µ+, µ-, and e+ accounting for the other• oneSiPM-third. Thereadout application (via of theﬁber) calorimeter and particle-identification criteria of Section 3.5.399.99% removes net the nonefﬁciency-electron tracks. (3 ofThe 4)e+ fail to satisfy the Δt requirement • - since they originate in the calorimeter and travel upstream through the tracker, the µ fail the particle-identification likelihood-ratio requirement, and the µ+ often fail both. In David Brown, LBNL 13 The Mu2e Experiment Tau 2014 addition some of the e+ and e- fail the E/p criteria because the calorimeter cluster includes energy from the interaction producing the electron or positron.

A total of 27.909 billion events were generated. This corresponds to a veto live time of 2.98 x 105 seconds, which is about 2% of the total veto live time [69]. Out of the generated events, 120,815 events could be reconstructed with a downstream electron hypothesis.

Table 3.3 below lists the number of events surviving the various requirements. It also lists the types of particles responsible for the reconstructed tracks. The production processes and the production volumes of the events surviving the track selection criteria are shown in Figure 3.33.

Fermi National Accelerator laboratory Mu2e Track Reconstruction

• GHz background rate, single track, no t0 ~1 μ-sec • Challenging pattern recognition problem! • Time division: deﬁne 3d points along the track • Need high efﬁciency, < 2‰ momentum resolution • Multi-stage solution μ-capture particle Robust Helix Fit Kalman Fit background removal (requires Time Division) (import from BaBar) Transverse Tracker Hit Position

14 David Brown, LBNL The Mu2e Experiment Tau 2014 Mu2e Signal Sensitivity

e- Recoil µ- ν ν

SES = 2.6×10-17

- - (stat errors only) e µ X

Reconstructed e- Momentum

David Brown, LBNL 15 The Mu2e Experiment Tau 2014 Mu2e Backgrounds

Category Source Events μ Decay in Orbit 0.21± 0.09 μ-Intrinsic Radiative μ Capture <0.01 Radiative π Capture 0.023±0.006

Beam electrons 0.003±0.001

μ Decay in Flight <0.003

π Decay in Flight <0.001 Out-of-Time Antiproton induced 0.047±0.024 Cosmic Ray induced 0.096±0.020 Other Pat. Recognition Errors <0.01 Total Background 0.37 ± 0.10 (assuming 6×1017 stopped muons in 6×107s of beam time) Discovery sensitivity achieved by suppressing backgrounds to <1 event total

David Brown, LBNL 16 The Mu2e Experiment Tau 2014 Mu2e Project Status • Critical path: Solenoid design, construction, commissioning

CD-3a CD-2/3

Fabricate and QA Superconductor

Solenoid Design

Solenoid Fabrication and QA

Start of Detector Hall Construction Solenoid Infrastructure Operations

Solenoid Installation and Commissioning

Detector Construction

Accelerator Accelerator and Beamline Construction Commissioning (off Project)

FY14 FY15 FY16 FY17 FY18 FY19 FY20 FY21

David Brown, LBNL 17 The Mu2e Experiment Tau 2014 Conclusions • μ→e is a powerful probe of New Physics • Sensitive to wide range of BSM models • Complimentary to direct searches • The Mu2e experiment will provide a 104 increase in sensitivity to muonic CLFV • SC cable fabrication begun • Commissioning to start in 2020 • Mu2e starts a new Physics Program at FNAL • Follow-on tests can explore model dependence • Factor of ~10 sensitivity increase with PIP-II

David Brown, LBNL 18 The Mu2e Experiment Tau 2014 Backup

Mu2e

David Brown, LBNL 19 The Mu2e Experiment Tau 2014 CLFV as a New Physics Probe • ν-oscillation induced Charged Lepton Flavor Violation (CLFV) has an un-observably small rate • Detection of CLFV would be a sign of New Physics • Many SM extensions predict CLFV

µ χ˜0 e µ˜ e˜

David Brown, LBNL 20 The Mu2e Experiment Tau 2014 Atomic Dependence

• Larger atomic Z→ V. Cirigliano et al., phys. Rev. D80 013002 (2009)

smaller bohr radius→ 4 lead larger capture Γ →

greater contact term titanium 3 aluminum Vector2 sensitivity

• = shorter μ lifetime 2 • Heavier nuclei→ Vector1 more neutrons→ 1 Dipole larger d/u fraction Scalar Z • Net result: Rμe is 0 model sensitive Z

David Brown, LBNL 21 The Mu2e Experiment Tau 2014 Mu2e Measurement Goal

1 10-1

10-3

10-5

-7 10 MEG 2013 arXiv:1303.0754 10-9

10-11

10-13 Mu2e Goal: -17 ~104 10-15 Rµe < 6×10 improvement @90% CL Mu2e 10-17

10-19 1940 1950 1960 1970 1980 1990 2000 2010 2020 2030

David Brown, LBNL 22 The Mu2e Experiment Tau 2014 Solenoidal Transport • Graded ﬁelds increase collection efﬁciency, sweep particles towards detector

4.5

2 T

1 T

14 meters David Brown, LBNL 23 The Mu2e Experiment Tau 2014 Production Solenoid • High ﬁeld, high radiation • Bronze shields superconductor • Tungsten rod target • Radiation cooled: 1650° C! • 0.005 μ- produced per POT • Radiation limit: Al stabilizer atom displacement < 10-5/year • Must anneal once/year! • Cable samples meet requirements 30 mm

Cross-section of Extruded PS Conductor

David Brown, LBNL 24 The Mu2e Experiment Tau 2014 Proton Pulse Formation • Re-bunching forms narrow pulses • ~200 nsec wide φ (deg) • out-of-time proton

fraction < 10-4

Current

• AC dipole deﬂects 200 nsec out-of-time protons Beam • 300 KHz + 3.8 MHz • resonant with beam • Additional factor of 10-7 rejection • Net ‘extinction’ of out- of-time protons < 10-10

David Brown, LBNL 25 The Mu2e Experiment Tau 2014 Other CLFV Processes • The most sensitive CLFV probes use muons

Process Current Limit Next Generation exp τ −−> µη BR < 6.5 E-8 τ −−> µγ BR < 6.8 E-8 10-9 τ −−> µµµ BR < 3.2 E-8 τ −−> eee BR < 3.6 E-8

KL BR < 4.7 E-12 K+ BR < 1.3 E-11 NA62 B0 BR < 7.8 E-8 Belle II, LHCb B+ BR < 9.1 E-8 µ+ BR < 5.7 E-13 10-14 µ+ BR < 1.0 E-12 10 µN --> eN R 10-17

5 David Brown, LBNL 26 The Mu2e Experiment Tau 2014 Active Extinction AC dipole driven with 300 • KHz + 3.8 MHz • Out-of-time protons < 10-10 M4 line

David Brown, LBNL 27 The Mu2e Experiment Tau 2014 Stopping Target • (17) 200 μm thick, ~10cm diameter Aluminum disks • Compromise between stopping power and e- straggling • ~105 stopped µ- each 1.7 μsec bunch

David Brown, LBNL 28 The Mu2e Experiment Tau 2014 Detector Solenoid

shielding 1 T DS ﬁeld 2 T

~ 6 m

• 2.0T→1.0T near target Target • ~50% increase in e- acceptance • 0.5 %/meter gradient in detector region • sweeps out slow e±, μ±

David Brown, LBNL 29 The Mu2e Experiment Tau 2014 Muon Beamstop • Absorbs muons with minimal backsplash • Stainless Steel + Poly shielding • Pinhole camera detects µ- atomic capture x-rays • Measures stopping rate • Requires high background tolerance and 152Eu good energy resolution • Possible detectors: • HPGe μ+Al (2P) 346 KeV • Lanthanum Bromide x-ray energy (KeV) David Brown, LBNL 30 The Mu2e Experiment Tau 2014 Neutron Background Mitigation

Neutrons come from several Heavy Concrete • sources in Mu2e • Primary target, collimators, μ stopping target, beamstop, ... • Neutrons affect the detectors • Radiation damage to SIPMs • Tracker and calorimeter hits Fake coincidences in CRV borated • polyethylene • Reduces conversion efﬁciency • Neutron mitigation: • Borated poly in the DS cryostat • Barite concrete outside

David Brown, LBNL 31 The Mu2e Experiment Tau 2014 DAQ • ‘Triggerless’ architecture Benchmark Tests • Raw data streamed to online Clock Distribution Readout Controler farm (36 servers) • Fast track ﬁnding ﬁlter • 1/500 reduction to disk 5ms/event, 400 Hz, 1Pb/year • >10 GBs Readout Server Optical Transciever Controler achieved Xeon-ES Xeon-Phi (32 cores/CPU) (120 cores/CPU) ...... Detector

× 543 × 36 190K events/sec 140K events/sec

(10G Ethernet switch) (meets spec) Event Building network David Brown, LBNL 32 The Mu2e Experiment Tau 2014 Track Finding and Fitting • Remove hits from low- energy electrons • Remove hits with large energy deposits (protons) • Select hits which peak in time • Fit in sequence: • Robust Helix • Least-squares • Kalman Filter

David Brown, LBNL 33 The Mu2e Experiment Tau 2014 + + Method 3: π →e νe Calibration • Stopped π+ produce a mono- energetic electron + + e π νe • line source calibration • Requires a special detector Reconstructed + Momentum conﬁguration π • Reversed selection collimator E. Barnes (BU) • Reduced (70%) magnetic ﬁeld • Reduced beam intensity Counts/100KeV • Earlier (< 300 nsec) event selection • Preliminary studies show <100 KeV accuracy possible Momentum (MeV) • ~1 day running time

David Brown, LBNL 34 The Mu2e Experiment Tau 2014 Mu2e Snowmass Studies • Assumes a ‘project-X’ type linear proton source • 1-3 GeV proton primary • ~150 KW power (3 × Mu2e instantaneous rate) • 100 ns (Gaussian) time spread -18 SES ~ 3×10 (×10 improvement) possible with modest experiment • upgrades • Follow-on studies to Mu2e: alternate target materials possible

arXiv:1307.1168 David Brown, LBNL 35 The Mu2e Experiment Tau 2014 Lots of Activity Going On!

Transport Solenoid – Al stabilized conductor

• After Hitachi completed the manufacturing of the requested 3000 m, all unit lengths were tested, reviewed and accepted on schedule by the end of October. The TS stabilized cable met all specifications. (critical current, copper RRR, Aluminum RRR, Aluminum yield, Cu-Al bonding strength, final cable geometry…)

16000 15000 TS_L1_Tail_CABLE_IC MeasurementMeasurement SetupSetup 14000 TS_L1_Tail_S1_no_SF 13000 TS_L1_Tail_S2_no_SF 12000

TS_L1_Tail_S1_SF_corr 11000 TS_L1_Tail_S2_SF_corr 10000 This setup is an improved version of a test experiment 9000 Cross-section of Al-Stabilized TS Cable after cold-work 8000 performed by part of this collaboration at PSI in 2009. 7000 The most of the equipments are already available. 6000 Critical Critical Current(A) 5000 TS cable I tested @ INFN Genoa 4000 c Trigger plastic and compared to extracted strands counter-1 3000 Target 2000 from etched cable Al 1000 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 Magnetic Field (T)

Trigger plastic counter-2 Charged particle detectors Si (t65µm) Si (t1500µm) plastic scinti. Pull tests were performed on every piece5 -length to check David Brown, LBNL Al-Cu bonding proprieties. 36 The Mu2e Experiment Tau 2014

8 KEK/J-PARC-PAC 2012-10

COMETCHAPTER 1. OVERVIEW 11 J-PARC • Pion Capture Section A section to capture pions with a large experiment, solid angle under a high solenoidal magnetic field by superconducting Production maget similar to Mu2e Target • Phase-1 COMET Phase-I Detector Section approved and A detector to search for muon-to-electron conver- under sion processes. Stopping construction Target Phase-1 • Pion-Decay and sensitivity: Muon-Transport Section A section to collect muons from -15 decay of pions under a solenoi- Rμe < 3.1×10 dal magnetic field.

年月日木曜日

Figure 1.1: Schematic layout of COMET and COMET Phase-I David Brown, LBNL 37 The Mu2e Experiment Tau 2014

C-shape muon transport in the muon beam • Instead of the S-shape that was adopted by a previously proposed experiment at BNL (MECO) [2], the C-shape muon transport in the muon beam line (from the pion production to the muon-stopping target) is chosen in COMET. This requires an additional compensating dipole ﬁeld, which can be produced using separate dipole coils or by tilting the solenoid coils. Since the muon momentum dispersion is propor- tional to a total bending angle, the C-shape beamline will produce a larger separation of the muon tracks as a function of momentum, resulting in improved momentum selection, which can also be varied independently of the solenoidal ﬁeld if separate dipole coils are employed.

C-shape electron transport in the detector • Instead of a straight solenoid, a C-shaped electron transport (from the muon-stopping target to the detector) is adopted in the COMET spectrometer. The principle of momentum selection is the same as that used in the muon transport system, but, in the spectrometer, electrons of low momenta which mostly come from muon decay in