μ-e Conversion Experiment with Pulsed Proton Beam ---DeeMe--- M. Aoki, Osaka University on behalf of DeeMe working group TRIUMF, Vancouver, 2010/4/28

DeeMe Collaboration JAERI KEK Osaka University TRIUMF UBC M. Kinsho M. Ikegami, S. Mihara, K. Yoshimura, N. Saito, H. Iinuma, H. Nishiguchi, C. Ohmori, M. Yoshii, K. Shimomura, N. Kawamura, S. Patrick, K. Nishiyama, M. Yoshida Osaka University M. Aoki, A. Sato, T. Itahashi, Y. Kuno TRIUMF T. Numao, J. Doornbos UBC D. Bryman

Contents J-PARC Introduction Muon in Particle Physics Charged Lepton Flavor Violation mN→eN Process Experiments Searching for mN→eN Process Principle of experiment A new idea J-PARC Test Measurements @ J-PARC MLF D2 DeeMe Single Event Sensitivity Background Summary

Standard Model of Particle Physics There are three generations (flavors) of Quarks and Leptons. Muon was found at 1936. I.I. Rabi said “Who ordered that?” Is the muon excited state of electron? The world-first search for muon rare process: m -> e g @1947 Null Result → a hint of generation BRtheory(m->eg)~10-4 @ 1958 But exp. already gave BRexp. < 2 x 10-5 → Two neutrinos model ne ≠ nm @1962 BNL Toward the establishment of the concept of “generation/flavor”. Muon played very important role in the development of particle physics.

Today, what do we know about generation (flavor) Quark Mixing Cabbibo-Kobayashi-Maskawa (CKM) Matrix Established --- Novel Prize@2008 Neutrino Mixing Pontecorvo-Maki-Nakagawa-Sakata (PMNS) Matrix Homestake, Kamiokande, SNO, T2K etc. Observed and Established. Charged Lepton Flavor Violation (CLFV) No observation yet at all. Implemented to the Standard Model of Particle Physics as “forbidden”. s b d u c t Quarks t e ne nm nt m ? Leptons

Charged Lepton Flavor Violation charged Lepton Flavor Violation (CLFV) Forbidden in the SM μ-+A→e-+A , μ→eγ, μ→eee, τ→e(μ)γ, τ→e(μ)h ... Neutrino-mixing predicts very small amount of CLFV via higher order diagram; it is as small as practically impossible to observe in foreseeable future. CLFV = Physics beyond SM with neutrino oscillation A. de Gouvea 7

History of CLFV Searches Since 1948 E.P. Hincks and B. Pontecorvo, PR 73 (1948) 257 m → e g: Concept of “Flavor” History of CLFV = History of particle physics. The best limits from muons. Current Limits m → e g: < 1.2 x 10-11 (MEGA) m-N → e-N: < 7x10-13(SINDRUM II) On-going program MEG/PSI m → e g: < 10-13 After Yoshitaka Kuno 8

SUSY and CLFV Standard Model ≠ “the theory of everything”. Hierarchy Problem Unification of Force Supersymmetry (SUSY) If SUSY exists → SUSY flavor mixing → CLFV 9

Golden Trio g-2 EDM m-LFV Real Imaginary slepton mass matrix τ-LFV

CLFV Predictions SUSY+Seesaw, MSW Large Angle tanβ=30 tanβ=10 tanβ=3 MEG SUSY+Seesaw, MSW Large Angle tanβ=3 tanβ=10 tanβ=30 DeeMe L. Calibbi, A. Faccia, A. Masiero and S.K. Vempati PRD 74(2006) 116002

m- + N → e- + N Muonic Atom (1S state) μ-e Conversion MC:MDO = 1:1000(H), 3:2(Al), 13:1(Cu) τ(free μ-) = 2.2 μs τ(μ-;Al) = 0.88 μs μ-e Conversion Muon Capture(MC) μ− nuclei Muon Decay in Orbit (MDO) charged Lepton Flavor Violation (CLFV) 13

Physics of μ-e Conversion SUSY-GUT, SUSY-seesaw (Gauge Mediated process) BR = 10-15 = BR(μ→eγ) × O(α) τ→lγ SUSY-seesaw (Higgs Mediated process) BR = 10-12~10-14 τ→lη Doubly Charged Higgs Boson (LRS etc.) Logarithmic enhancement in a loop diagram for μ-N → e-N, not for μ→e γ M. Raidal and A. Santamaria, PLB 421 (1998) 250 SUSY with R-parity Violation Leptquarks Heavy Z’ Compositeness Multi-Higgs Models N N

Principal of Experiment SINDRUM II Signal : μ- +(A,Z) → e- +(A,Z) A single mono-energetic electron 105 MeV Delayed：~1μS No accidental backgrounds Physics backgrounds Muon Decay in Orbit (MDO) Ee > 102.5 MeV (BR:10-14) Ee > 103.5 MeV (BR:10-16) Beam Pion Capture π-+(A,Z) → (A,Z-1)* → γ+(A,Z-1) γ → e+ e- Prompt timing BR[Al] < 7 × 10-13 15

SINDRUM-II PSI/πE5 SINDRUM II 16

SINDRUM II (2) Need more muonic atoms: >1010 μ-/s. Beam-induced prompt backgrouds: Pulsed beam. Detector rate might be too high: Some Ideas to reduce it. BR < 7 × 10-13 17

CLFV and Related Programs FNAL: BR(μ- N → e- N) < 10-16 FNAL: μ g-2 < 0.1 ppm LHC: SUSY Search Bs → μ+μ-, Bs → τμ, τ → μμμ KEKB: τ → e(μ) γ, τ → e(μ) η ... BR < 10-8 BNL: μ g-2 < 0.5 ppm >3-σ off from SM PSI/MEG: BR(μ → e γ) < 10-13 J-PARC: BR(μ- N → e- N) < 10-14 , 10-16 J-PARC: μ g-2 < 0.1 ppm PSI: μ EDM J-PARC: μ EDM

General Idea of μ-e Conversion Setup Sensitivity High m- yield Background Pulsed Proton Detector Rate Momentum Selection before Detector

μ-e electrons may directly coming from a production target. → DeeMe an electron analogue of the surface muon. the same idea by Doug Bryman and Toshio Numao, independently Experiment could be very simple, quick and low-cost.

Test Measurement How many m- actually stop in the muon target? What is the potential source of backgrounds. → Test Measurement at J-PARC MLF, Tokai, Japan J-PARC @ Tokai, Japan

J-PARC LINAC RCS MR H-, 400 MeV, 50 mA 50 Hz 3 GeV, 333 μA 25 Hz Vancouver Tokai, Japan LINAC H-, 400 MeV, 50 mA 50 Hz RCS 3 GeV, 333 μA 25 Hz Fast Extraction Material and Life-science Facility (MLF) MR 30 GeV, 15 μA Fast and Slow EX

J-PARC MLF Muon Facility 3-GeV Proton

Test Measurement at D2 How many m- actually stop in the muon target? What is the potential source of backgrounds. Muonic Atom Formation Rate Measurement Yield of Michel e- from target. Decay constant of e- e- from carbon: 2.0 msec Otherwise, << 2.0 msec Extinction Ratio Measurement Time structure of high momentum e- (Ee- > 52 MeV)

D2 Beamline Geometrical Acceptance: 45--60 msr Momentum Bite: 3%r.m.s. Beamline Length: ~40 m Surface muon yield ~160 kHz @ 17 kW protons

Detector for the Test Meas. Pb (4mmt) Plastic Scintillator D2 Exit B1: gating-PMT readout B2: gating-PMT readout B3: ND filter (1/1000), normal PMT readout μ- e- B1 B2 B3 Should detect delayed e- after prompt burst (>104/pulse) Beam time approved is very short → Use gating-PMT to increase delayed-time detection efficiency. Background e- coming from the decay of prompt m- stopped in counters. → Pb plate to absorb m- by muon capture process. Electron-detection efficiency ~ 50%

gating PMT No. of particles in a prompt pulse ~1e5 Standard PMT is saturated. Used a gating PMT system off/on gain ratio = 1e6 Designed by Taniguchi

Snapshot of PMT signal B1 Plas. Scinti. gating B2 B3 normal PMT ND filtered Baseline distortion due to delayed fluorescence from plastic scintillator. Individual hits by real particles can be seen on the baseline.

Result Intrinsic Counter Efficiency:~100% τ=2.10±0.02 μsec Potential contamination of e- from Bhabha scattering of e+ from m+ decay. But only order 2 at most. Existence of Michel Edge: confirmed The shape of spectrum is consistent with that obtained with G4Beamline Simulation. → e- from Muonic Carbon Atom: Confirmed Yield: 4.4 counts/pulse/100-kW @ detector Ne+/Ne-@40-MeV/c = 450 B1 pulse height (B2 tagged) B2 pulse height (B1 tagged)

G4Beamline Estimation G4Beamline model of D2 beam line 28 MeV/c μ- Geometrical Acceptance:40 msr Yield: 4.4 counts/pulse/100-kW @ detector → 8 × 109 /sec/MW in the Muon Production Target.

Sensitivity w/ current D2 D2 and the current muon target RμC = 8 × 109 sec/MW D2 Acceptance: 0.04% @ 105 MeV/c Muon Capture Rate(Carbon) = 0.08 Time Window Acceptance = 66% μ-e relative strength (normalized to Al) = 0.7 Running Time 107 sec S.E.S. = 8 × 10-13 [Al equivalent] SINDRUM II limit = 7 × 10-13 Not impressive. Do not worry. This is not an end of story.

Sensitivity w/ a new Beamline Place Al μ-stopper: Capture rate 0.08 → 0.60 New Beam line with larger acceptance: x4 Exclusive use of the New Beam line: x2 or more S.E.S < 10-14 for Al π- μ-

Concept of the New BL Concept by Jaap Dornbos (TRIUMF) Detailed Design is on-going. Solenoid focusing + dipole for bend The first Solenoid could be a single type. Kicker to reduce prompt burst 1/1000 Spec: J-PARC RCS type is OK Acceptance = 140 msr Δp/p = 10 MeV/c(FWHM) H line

Backgrounds How much difficult to achieve the extinction 10-14? Should Delay by ~msec ** Only coming from μ decay.** Background: Muon Decay in Orbit : mostly Ee < 55 MeV NDIO < 10-14: Ee > 102.5 MeV Signal: μ-e Electron: Pe = 105 MeV/c If there is any off-timing protons, that could become potential background. Extinction < 10-14 Rextinction[COMET] < 10-9, Rπ-survive[COMET] = 10-5 How much difficult to achieve the extinction 10-14? Fast Extraction No scattering by septum during the slow extraction. Fall time of kicker is very fast. < 300 nsec. There is a room to install additional kickers in the primary beam line.

DeeMe @ J-PARC MLF Sensitivity Schedule DeeMe <10-14 ~2015 new dedicated beamline high-power pulsed proton beam mu-e conversion Sensitivity Schedule DeeMe <10-14 ~2015 COMET/Mu2E <10-16 2017~

Summary A new idea of m-e conversion experiment (DeeMe) that could improve the current limit by 2 orders of magnitudes (BR < 10-14) was shown. Test Measurement at J-PARC MLF D2 was performed. The time constant of e- from D2 is consistent with m- decay in carbon. The shape of spectrum is consistent with Michel Spectrum. The rate of muonic carbon atom formation is 8 × 109 /sec/MW @ Muon Target Very good agreement with Geant4 MC: 7 × 109 /sec/MW The extinction should be < 10-14, which would be a severe requirement. But, Fast-extracted beam should have much better extinction than slow-extracted beam. Extra Extinction Kicker (The same type as the current RCS kicker) can be located in the primary beam line. Expression of Interest (EoI) is open to the public. Working for the detailed design of experiment. See http://deeme.hep.sci.osaka-j.ac.jp for more information.