M. Aoki Translation of slides in 2010 JPS meeting (Okayama) By K. Shimomura and M. Aoki M. Aoki A ， T. Ebihara A ， N. Kawamura ， Y. Kuno A ， P. Strasser ， N. Nakadozono A ， H. Nishiguchi ， K. Nishiyama ， T. Numao B ， T. Hikida A ， E. Matsushita A ， S. Mihara ， Y. Miyake ， K. Yoshimura KEK ， Osaka U. A ， TRIUMF B Measurement of Muonium Yield

MLF Beam Test Measurement of the Yield of Muonic Atom. By measuring electrons from the decay of the muonic atom. The time spectrum of the electrons should be the same to that of the life time of μ - in carbon (2.0 μs). The momentum spectrum of the delayed electrons should be like that of Michel spectrum. Performed at D2 in J-PARC MLF 2009A0023: 3 days 2009A0032: 1 day

D2 Beam line at J-PARC MLF 3 D2 Port Designed for the decay-muon maximum momentum: 120MeV/c → can extract 105MeV/c electrons. Muon Target Proton Beam Neutron Target Superconducting Solenoid

Surface muon extraction by D2 Beam line 4 p ++ ++ Surface Muon μ + (4MeV, 30MeV/c) from the decay of π + stopped in the production target. no surface μ - since the parent π - is promptly captured by nucleus. TRANSPORT,TURTLE

Separation of positrons and muons by TOF 5 PositronMuon 200ns Beam Line 28.6m Can be used to calibrate the muon momentum.

Surface Muon: momentum scan and yield 6 Drop by the window material dE by the window material ~ 1 MeV/c Yield (Measurement) (by counting the Michel positrons ） 1.5×10 7 /s(for 1MW of proton) Yield(MC) 1.8×10 7 /s(1MW) Momentum Acceptance ~6 ％ (FWHM) The beamline acceptance is well understood.

7 G4Beamline Estimation 28 MeV/c μ - G4Beamline model of D2 beam line Geometrical Acceptance:30 msr for point source

Detector for the Test Meas. D2 Exit Pb (4mm t ) Plastic Scintillator μ-μ- e-e- B1B2B3 B1: gating-PMT readout B2: gating-PMT readout B3: ND filter (1/1000), normal PMT readout Have to detect delayed e - after prompt burst (>10 4 /pulse). Beam time approved is very short → Use gating-PMT to increase delayed-time detection efficiency. Background e - coming from the decay of prompt  - stopped in counters. → Pb plate to absorb  - by muon capture process. Electron-detection efficiency ~ 50%

gating PMT No. of particles in a prompt pulse ~1e4 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 Plas. Scinti. gating B3 Plas. Scinti. normal PMT ND filtered Baseline distortion due to delayed fluorescence from plastic scintillator. Individual hits by real particles can be seen on the baseline.

B1 pulse height (B2 tagged) B2 pulse height (B1 tagged)

Time Spectrum e - from Bhabha scattering of e + from μ + decay. N e+ /N = 450 Dominate in P e < 30 MeV/c e-e- e - from e + scattering MC simulated momentum spectra e-e- e - from e + scattering

Mom. Spectrum p e > 40 MeV/c: Dominated by e - from μ - decay. p e ~ 50 MeV/c: Michel Edge p e < 30 MeV/c: Dominated by e - from e + scattering where the e + is coming from μ + Michel decay. → μ - stopping rate = 6 × 10 9 /sec/MW in the current fixed Target. e-e- e - from e + scattering

π - production 2e13/MW For 20-mm graphite = 0.9 mb 0.95 < θ < GeV/c < p < 0.15 GeV/c HARP: 0.4 mb Geant4 (QGSP_BERT_HP) Good agreement with HARP Especially p < 200 MeV/c region

Yield with the Rotation Target mm outer r mm outer r