After-Proton background estimation for the DeeMe experiment 大阪大学久野研究室 M2 Daiki Nagao 1
OUTLINE DeeMe experiment • After-Proton background • After-Proton counter • Analysis • Summery • 2
DeeMe experiment DeeMe is the µ-e conversion searching experiment at J-PARC MLF ν e ν μ ν τ µ-e conversion e μ τ One of charged Lepton Flavor Violation (cLFV) • − + ( A , Z ) → e − + ( A , Z ) µ Forbidden in the Standard Model (SM) • • Theories beyond the SM predict the µ-e conversion at the branching ratio level of ~10 -14 Mono-energetic electron (105MeV/c) • µ e Nucleus Delayed signal (~ 1µs) • Muonic atom 3
production target DeeMe experiment in production target 1. π production proton 2. µ production 3. muonic atom π formation µ 3GeV Rapid Cycling 4. µ-e conversion Synchrotron (RCS) e 物質・生命科学 MLF H-Line 実験施設（ MLF ） J-PARC Single event sensitivity = 10 -14 (with SiC target) • • Different way to search the µ-e conversion from COMET and Mu2e • The beam energy is 3 GeV • no background from proton pair production • duty factor = 1/20000 • lesser cosmic lay background • Measurement start from 2016
DeeMe experiment DIO Measurement The momentum distribution of µ-e electrons and backgrounds by Monte Carlo simulation µ -e signal Decay In Orbit (DIO) = e - decayed from µ - in the muonic atom by µ − → e − + ν e + ν µ After-Proton Pulsed proton beam from RCS 600ns • Repetition 25Hz 40ms Fast extraction • • No residual protons in No protons No protons kicker magnet off timing // Pulsed proton 5
DeeMe experiment • The signal electrons will be observed in delayed timing from pulsed proton. • Measurement time is about 2µs. 600ns 40ms Primary Proton // Measurement e - signals 1µs 2µs // = prompt burst +DIO electrons + µ-e signal 6
After-Proton background If there are protons delayed from main pulse, they may hit the production target. • • Produced prompt burst → After-Proton background After Proton Primary Proton // Measurement e - signals // = prompt burst +DIO electrons + µ-e signal 7
After-Proton background The prompt electrons produced by protons will be able to have the same • momentum as µ-e conversion electrons • It might be difficult for our spectrometer to distinguish the After-Proton background from the signal if such a background exists. DIO Measurement µ -e signal After-Proton The momentum distribution of µ-e electrons, DIO BG and After-Proton BG 8
After-Proton counter After-Protons R AP = ———————— Definition • Total protons R AP < 10 -18 will be required in DeeMe experiment • According to a Monte Carlo simulation, • hit BLM × 40 = delayed protons RCS extraction region Beam loss monitor (BLM) ⇒ The BLM was set up in RCS tunnel septum magnets To MLF / MR RCS ring proton beam 9
Fe absorber After-Proton counter The BLM had 2 scintillation counter and Fe absorber • the time spectrum AP 解析‐清水宏祐 Fe absorber (10cm thickness) It imply that there are some contamination by positrons decayed from the rest muons particle efficiency 3GeV proton 0.98 scintillation counters Michel positron 0.04 10
Analysis It can be improved by suppression of the positrons 11 calculated by H. Shimizu
New After-Proton counter e+ π protons Beam Line µ e+ 10mm 10mm 10mm 16mm 32mm 16mm 32mm Pb sci1 Pb sci2 Pb sci3 Pb According to a G4beamline simulation, a lead-scintillator sandwich counter as the above • picture eliminate the Michel positron more than before one. efficiency (3GeV proton): 90~95% • suppression (e+): 2 × 10 -4 ~ 6 × 10 -5 • This counter was set up in the RCS in January, 2015 • 12
Data taking • Data taking with 500-MHz flash ADC • waveform length = 8µs • Trigger signal is synchronized with the beam extraction timing to MLF. • The beam position monitor(BPM) monitors the protons in the RCS ring duct. • The fluctuation of extraction timing is corrected with the BPM signal. ch0 -2.7kV ch1 -2.0kV ch2 -1.6kV BPM 13
New counter with MLF trigger TDC histograms coincidence TDC histogram 14
waveform with MR trigger MR extraction trigger The beam to MLF was stopped from last month. • Taken data with MLF trigger are too little • (~30,000 events) to calculate the performance of the counter. performance check with MR extraction trigger • MR extraction • trigger rate = ~1Hz • beam extraction timing extraction timing is not constant • Difference between MR and MLF extraction • the number of protons in a bunch • emittance • beam halo • 15
MR extraction trigger Time distribution TDC (3 counters coincidence) • 16
Calculation of the suppression (New counter) single counter coincidence f ( x ) = p 0 × exp( − t ) + p 2 p 1 Total hits = 2.811 x 10 5 Constant = p 2 x 360 = 130.3 x 360 Total hits = 16 exp. hits = 2.811 x 10 5 - 130.3 x 360 = 2.342 x 10 5 coincidence / single = 16 / 2.342 x 10 5 = 6.8 x 10 -5 17
Calculation of the suppression (Fe absorber counter) single counter coincidence f ( x ) = p 0 × exp( − t ) + p 2 p 1 Total hits = 1.269 x 10 5 Constant = p 2 x 360 = 252.9 x 360 Total hits = 51 exp. hits = 1.269 x 10 5 – 252.9 x 360 = 3.586x 10 4 coincidence / single = 51 / 3.586x 10 4 = 1.4 x 10 -3 18
Calculation of the suppression New BLM Fe absorber BLM coincidence / single = 6.8 x 10 -5 coincidence / single = 1.4 x 10 -3 The single PMT hit rates of each BLM are the same, the suppression of the new BLM looks increasing. 19
Summery DeeMe is the µ-e conversion searching experiment • • µ-e conversion is one of cLFV • After-Protons are protons delayed from main pulse • They may produce the prompt burst • New counter installed in RCS tunnel is working • New BLM is expected to increase the suppression of the positrons ~ 10 -2 • The suppression of the positrons looks increase with MR trigger • The BLM may be able to be more optimized 20
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