Mu2e experiment at Fermilab Yuri Davydov DLNP, JINR, Dubna Erevan, March 2015.

Mu2e experiment at Fermilab Yuri Davydov DLNP, JINR, Dubna Erevan, March 2015

Introduction What is Mu2e? A search for Charged-Lepton Flavor Violation via Will use current Fermilab accelerator complex to reach a sensitivity 10 000 better than current worlds best Will have discovery sensitivity over broad swath of New Physics parameter space 2 - N e - N March 2015

Flavor Violation Weve known for a long time that quarks mix (Quark) Flavor Violation In last 15 years weve come to know that neutrinos mix Lepton Flavor Violation (LFV) Why not Charged Lepton Flavor Violation (CLFV)? 3March 2015

CLFV in the Standard Model Strictly speaking, forbidden in the SM Even in -SM, extremely suppressed (rate ~ m 2 / M w 2 < 10 -50 ) However, most all NP models predict rates observable at next generation CLFV experiments 4 q q e-e- W e March 2015

5 Mu2e : SM prediction and New Physics The BR of CLFV processes in the Standard Model Flavour Physics of Leptons and Dipole Moments, Eur.Phys.J.C57:13-182,2008 NP Sensitive to mass scales up to O(10,000 TeV) Mu2e sensitivity is 6*10 -17 March 2015

Mu2e High Priority for U.S. HEP In the 2008 P5 report Mu2e was strongly supported: Mu2e should be pursued in all budget scenarios considered by the panel In 2010 P5 reiterated their support of the 2008 plan and the priorities specified therein. In 2013 the Facilities Panel gave Mu2e the highest endorsement: The science of Mu2e is Critical to the DOE OHEP mission and is Ready to Construct. In the 2014 P5 report Mu2e is strongly supported: Recommendation 14, Complete the Muon (g-2) and Mu2e Projects. March 20156

How does Mu2e work? March 20157

8 Mu2e Concept Generate a beam of low momentum muons ( Stop the muons in a target Mu2e plans to use aluminum Sensitivity goal requires ~10 18 stopped muons The stopped muons are trapped in orbit around the nucleus In orbit around aluminum: Al = 864 ns Large N important for discriminating background Look for events consistent with N eN March 2015

9 Mu2e Signal The process is a coherent one The nucleus is kept intact Experimental signature is an electron and nothing else Energy of electron: E e = m - E recoil - E 1S-B.E. For aluminum: E e =104.96 MeV Important for discriminating background March 2015

Mu2e Sensitivity Design goal: single-event-sensitivity 2.4 x 10 -17 Requires about 10 18 stopped muons Requires about 10 20 protons on target Requires extreme suppression of backgrounds Expected limit: R e < 6 x 10 -17 @ 90% CL Factor 10 4 improvement Discovery sensitivity: all R e > 1 x 10 -16 Covers broad range of new physics theories March 201510

The great-grandparents of the Mu2e ( MELC, 1992; MECO, 1997) V.M. Lobashev and R.M. Djilkibaev 11March 2015 -e conversion experiment concept

Baseline Mu2e Apparatus Particles produced from tungsten target Muons stop on Al target, which emits an electron isotropically 12 Tracker/calorimeter detect electron signature S-shaped solenoid: transports particles to detector area, and allows remaining pions to decay to muons collimator selects negatively-charged particles 8-GeV protons from delivery ring 4.6 T 2.5 T 2.0 T 1.0 T Detector Region: Uniform Field 1T Graded B for most of length ( about 25 meters end-to-end March 2015

13 The Measurement Method E e = m - E recoil - E 1S-B.E. E e =104.96 MeV

Some Mu2e numbers Every 1 second Mu2e will Send 7,000,000,000,000 protons to theProduction Solenoid Send 26,000,000,000 s through the Transport Solenoid Stop 13,000,000,000, s in the Detector Solenoid By the time Mu2e is done Total number of stopped muons 1,000,000,000,000,000,000 March 201514

15 Mu2e Proton Beam Mu2e will use a pulsed proton beam and a delayed live gate to suppress prompt backgrounds 0 500 1000 1500 2000 2500 3000 3500 Time (ns) Proton pulse on Production target Muons at Stopping target 1700 ns 700 ns900 ns Live Window March 2015

The Mu2e Tracker Will employ straw technology Low mass Can reliably operate in vacuum Robust against single-wire failures 16 5 mm diameter straw Spiral wound Walls: 12 m Mylar + 3 m epoxy + 200 Au + 500 Al 25 m Au-plated W sense wire 33 117 cm in length 80/20 Ar/CO2 with HV < 1500 V March 2015

The Mu2e Tracker Self-supporting panel consists of 100 straws 6 panels assembled to make a plane 2 planes assembled to make a station Rotation of panels and planes improves stereo information >20k straws total 17 panel planestation March 2015

The Mu2e Tracker 18-20 stations with straws transverse to beam Naturally moves readout and support to large radii, out of active volume 18 3 meters 38 cm 70 cm March 2015

The Mu2e Tracker Inner 38 cm is purposefully un-instrumented Blind to beam flash Blind to >99% of DIO spectrum 19 Escape thru center of Tracker Fully fiducial March 2015

Mu2e Calorimeter Crystal calorimeter Compact Radiation hard Good timing and energy resolution 20March 2015

Mu2e Calorimeter Baseline design : Barrium Flouride (BaF 2 ) Radiation hard, very fast, non-hygroscopic 21 BaF 2 Density (g/cm3)4.89 Radiation length (cm)2.03 Moliere Radius (cm)3.10 Interaction length (cm)30.7 dE/dX (MeV/cm)6.52 Refractive index1.50 Peak luminescence (nm)220 (300) Decay time (ns)1 (650) Light yield (rel. to NaI)5% (42%) Variation with temperature0.1% (-1.9)% / deg-C March 2015

Mu2e Calorimeter Will employ 2 disks ( radius = 36-70 cm) ~2000 crystals with hexagonal cross-section ~3 cm diameter, ~20 cm long (10 X 0 ) Two photo-sensors/crystal on back (APDs or SiPMs) 22 Disk 1 Disk 2 March 2015

Mu2e Cosmic-Ray Veto Veto system covers entire DS and half TS 23 PS TS Without the veto system, ~1 cosmic-ray induced background event per day March 2015

Mu2e Cosmic-Ray Veto Will use 4 overlapping layers of scintillator Each bar is 5 x 2 x ~450 cm 3 2 WLS fibers / bar Read-out both ends of each fiber with SiPM Have achieved > 99.4% (per layer) in test beam 24March 2015

Backgrounds Stopped Muon induced Muon decay in orbit (DIO) Out of time protons or long transit-time secondaries Radiative pion capture; Muon decay in flight Pion decay in flight; Beam electrons Anti-protons Secondaries from cosmic rays 25 Mitigation: Excellent momentum resolution Excellent extinction plus delayed measurement window Thin window at center of TS absorbs anti-protons Shielding and veto March 2015

CategorySourceEvents Decay in Orbit 0.20 Intrinsic Radiative Capture

27 Mu2e Intrinsic Backgrounds Once trapped in orbit, muons will: 1)Decay in orbit (DIO): N --> e - e N For Al. DIO fraction is 39% Electron spectrum has tail out to 104.96 MeV Accounts for ~55% of total background March 2015

28 Mu2e Intrinsic Backgrounds Once trapped in orbit, muons will: 2)Capture on the nucleus: For Al. capture fraction is 61% Ordinary Capture N Z --> N * Z-1 Used for normalization Radiative capture N Z --> N * Z-1 + (# Radiative / # Ordinary) ~ 1 / 100,000 E kinematic end-point ~102 MeV Asymmetric -->e + e - pair production can yield a background electron March 2015

670 ns 925 ns 1695 ns Prompt Background Suppression Prompt background Happens around the time, when the beam arrives at the target. Sources beam electrons, muon decay in flight, pion decay in flight, radiative pion capture May create electrons with energies in the signal region Prompt background can be suppressed by not taking data during the first 670 ns after the peak of the proton pulse. However, this prompt background cannot be eliminated entirely, since some of the protons arrive out of time. A ratio of 10 -10 is required for the beam between pulses vs. the beam contained in a pulse. 29 The lifetime of a muon in an Al orbit is 864 ns March 2015

30 Mu2e Late Arriving Backgrounds Contributions from Radiative Capture N Z --> N * Z-1 + For Al. R C fraction: 2% E extends out to ~m Asymmetric e + e - pair production can yield background electron Beam electrons Originating from upstream and decays Electrons scatter in stopping target to get into detector acceptance Muon and pion Decay-in-Flight Taken together these backgrounds account for ~10% of the total background and scale linearly with the number of out-of- time protons March 2015

SourceEventsComment decay in orbit (DIO)0.20 0.06 Anti-proton capture0.10 0.06 Radiative - capture*0.04 0.02From protons during detection time Beam electrons*0.001 0.001 decay in flight*0.010 0.005With e - scatter in target Cosmic ray induced0.050 0.013Assumes 10 -4 veto inefficiency Total0.4 0.1 * scales with extinction: values in table assume extinction = 10 -10 All values preliminary; some are stat error only. Backgrounds for 3 Year Run 31March 2015

32 Mu2e Miscellaneous Backgrounds Several additional miscellaneous sources can contribute background - most importantly: Anti-protons Proton beam is just above pbar production threshold These low momentum pbars wander until they annihilate A thin mylar window in beamline absorbs most of them Annihilations produce high multiplicity final states e.g. can undergo R C to yield a background electron Cosmic rays Suppressed by passive and active shielding DIF or interactions in the detector material can give an e - or that yield a background electron Background listed assumes veto efficiency of 99.99% March 2015

Signal Sensitivity for 3 Year Run Reconstructed e - Momentum ~ 4x10 20 protons on target (3 year run @ 8 KW) Stopped : 10 18 N e = 3.94 0.03 For R = 10 -16 N DIO = 0.20 0.06 N Other = 0.2 SES = (2.5 0.1) 10 -17 Errors are stat only 33March 2015

34 LYSO 5x5 matrix beam tests

JINR CONTRIBUTION (1) March 201535 Mu2e Electromagnetic calorimeter Evaluation of crystal samples including LGSO, LSO, LYSO, BaF2 and CsI. Tests of the crystals on the gamma sources, cosmic muons and accelerator beams. Tests of the optical uniformity, scintillation yield and yield collection uniformity. Upgrade of the facility for the crystal testing at DLNP JINR. Simulation of the electromagnetic calorimeter elements and calorimeter in whole. Participation in the radiation hardness of the crystal and front-end electronic tests on the neutron sources of JINR and/or collaborator institutes. Participation in the production of crystals for the experiment in cooperation with Kharkov. Participation in quality control of the crystals by testing their performance. Participation in calorimeter construction and integration in the full detector on the experimental site. Maintenance of the calorimeter during the data taking period to ensure efficient operation.

JINR CONTRIBUTION (2) March 201536 Mu2e Cosmic Ray Veto system Participation in the simulation activity of Mu2e experiment to define the final demands to Cosmic Ray Veto system and choose the optimal geometry of this system. Upgrade of the facility for scintillation counters tests at DLNP JINR and Fermilab. Design, build and test the prototype scintillation counters for Cosmic Ray Veto system at the created stands. Participation in the prototype scintillator counters tests on the neutron facilities of JINR and/or collaborator institutes to define sensitivity of neutron registration and radiation hardness. Participation in the mass production and tests of the scintillation counters for Cosmic Ray Veto system in the cooperation with Kharkov, Fermilab and University of Virginia (UVA). Participation in the CRV test stand construction at Fermilab. Participation in the CRV construction and integration in the full detector on the experimental site. Maintenance of this system during the data taking period to provide its efficient operation.

JINR CONTRIBUTION (3) 37March 2015

Experimental setups for crystals and strips tests March 201538

LYSO SICCAS: 22 Na, coincidence Two left frames: linear scales, the bottom frame shows 1275 keV and 511+1275 keV sum peaks Right bottom frame shows spectrum in log scale along with peaks fitted with Gaussian 39

JINR Mu2e: Comparison of 3 crystals - Energy resolution and Linearity of the energy response

Sample from ISMA NASU * with triangular cross-section and inner hole 41 Geometry for the our strip sample: Base:33 mm Height:17 mm Length:2000 mm * ISMA NASU Institute for Scintillation Materials, National Academy of Sciences of Ukraine For water-filling holes were drilled in the side faces of the sample and plugs are made (see photo). The triangle scintillation strips with a hole in the center (diam. 2.6 mm) are similar to those developed for MINERvA Water-filling hole plug Fiber end

42 T EST CONDITIONS M EASUREMENTS OF THE LIGHT YIELDS FOR THE SAME SAMPLE OF THE SCINTILLATION STRIP WITH / WITHOUT DISTILLED WATER INSIDE WERE DONE ; L IGHT COLLECTED BY USING D = 1.2 MM K URARAY WLS FIBER. T HE STRIP S FAR END WAS COVERED BY A LUMINUM FOIL, NEAR END WAS CLOSED BY BLACK PLASTIC CAP FOR LIGHT ISOLATION. J UST HOLE LEFT FOR COUPLING THE WLS FIBER TO THE PMT; T HE WLS FIBER WAS INSERTED INTO THE HOLE AND FIXED BY GLUE ON BOTH ENDS ; D ISTILLED WATER PUMPED THROUGH THE SAMPLE, NO AIR BUBBLES WERE OBSERVED. PMT EMI 9814B WAS USED, HV= 2200 V. F OUR PAIRS OF TRIGGER COUNTERS WERE USED ; A BSOLUTE CALIBRATION METHOD WAS USED TO CALCULATE THE LIGHT YIELD 2 2 4

Results: comparison of the light collected of the same sample using the wls fiber with/without water 43 Fit function f(x)=exp p0+p1*x Measuring points () : 71.5 111.5 151.5 191.5 Increase of the yield of light (%) : 51 54 53 44

Some publications March 201544 L. Bartoszek et al., Mu2e Technical Design Report, arXiv:1501.05241 (2015). K. Afanaciev et al., Response of LYSO:Ce scintillation crystals to low energy gamma- rays, Particles and Nuclei, Letters, 2015, issue 2. G. Pezzullo et al., Progress status for the Mu2e calorimeter system, Journal of Physics: Conference Series 587(2015), 012047. G. Pezzullo et al., The LYSO crystal calorimeter for the Mu2e experiment, 2014 JINST 9 C03018. O. Sidletskiy et al., Evaluation of LGSO:Ce scintillator for high energy physics experiments, Nucl. Instr.&Meth. A735(2014) 620-623. J. Budagov et al., The calorimeter project for the Mu2e experiment, Nucl. Instr.&Meth. A718(2013) 56-59. Z. Usubov, Light output simulation of LYSO single crystal, arXiv:1305.3010 (2013). Z. Usubov, Electromagnetic calorimeter simulation for future e conversion experiments, arXiv:1212.4322 (2012).arXiv:1212.4322 R.J. Abrams et al., Mu2e Conceptual Design Report, arXiv:1211.7019 (2012).arXiv:1211.7019

March 201545 CD-1 CD-3a CD-2/3 Superconductor R&D Solenoid Infrastructure Solenoid Installation Install Detector Fabricate and QA Superconductor Solenoid Design Solenoid Fabrication and QA Mu2e Technical Schedule FY13 FY14 FY15 FY16 FY17 FY18 FY19 FY20 Accelerator and Beamline Detector Construction Field Mapping Detector Hall Design Site Work Detector Hall Construction Operations

What next? A next-generation Mu2e experiment makes sense in all scenarios Push sensitivity or Study underlying new physics Will need more protons upgrade accelerator 46 Precision Measurement if necessary Measure conversion rate as a function of Z Higher Sensitivity search Mu2e Signal? Yes No Accelerator Upgrade Accelerator Upgrade March 2015

Summary The Mu2e experiment: Improves sensitivity by a factor of 10 4 Provides discovery capability over wide range of New Physics models Is complementary to LHC, heavy-flavor, and neutrino experiments 47March 2015

48 BACKUP March 2015

Mu2e / COMET comparisonMu2eCOMET approval/ funding ranked among the very top priorities for the U.S. HEP program P5 Report 2014 Complete the Mu2e and g-2 projects. Mu2e is fully funded in all budget scenarios The DOE is committed to completing Mu2e COMET phase-II funding has not been identified and Japan has clearly stated that their top priorities are Belle-II, long baseline neutrinos, and ILC OperationCondition Mu2e will run simultaneously with NOvA and the short-baseline neutrino program at Fermilab COMET cannot run simultaneously with the JPARC neutrino program. It forces COMET to plan for higher beam power in order to minimize the amount of required beam time Detector Straight Solenoid with gradient field Tracker and Calorimeter C-shape Solenoid with gradient field Tracker and Calorimeter Because the Mu2e DS is straight, it is equally sensitive to e- and e+ and thus have an additional physics channel - N e + N and will be able to measure in situ some background components (e.g. - N N e - e + N) the COMET solenoids, particularly their production solenoid, is more technically risky (e.g. they will use a 9 (!) layer coil, Mu2e is 3 layer). March 201550

51March 2015

Mu2e / COMET comparison Mu2e has consistently been ranked among the very top priorities for the U.S. HEP program P5 Report 2008 Facilities Report 2012 P5 Report 2014 Complete the Mu2e and g-2 projects. Mu2e is fully funded in all budget scenarios The DOE is committed to completing Mu2e COMET phase-II funding has not been identified and Japan has clearly stated that their top priorities are Belle-II, long baseline neutrinos, and ILC Mu2e solenoids are technically less risky and employ fabrication and cooling techniques that have been used before the COMET solenoids, particularly their production solenoid, is more technically challenging (e.g. they will use a 9 (!) layer coil, Mu2e is 3 layer). March 201552

53 Status of CLFV Searches March 2015

Mu2e experiment at Fermilab Yuri Davydov DLNP, JINR, Dubna Erevan, March 2015.

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