After-Proton background estimation for the DeeMe experiment M2 - - PowerPoint PPT Presentation

大阪大学久野研究室M2 Daiki Nagao

After-Proton background estimation for the DeeMe experiment

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OUTLINE

• DeeMe experiment
• After-Proton background
• After-Proton counter
• Analysis
• Summery

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µ-e conversion

• One of charged Lepton Flavor Violation (cLFV)
• 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)
• Delayed signal (~ 1µs)

Nucleus

µ e Muonic atom

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DeeMe experiment

DeeMe is the µ-e conversion searching experiment at J-PARC MLF

νe νμ ντ e μ τ

µ

− +(A,Z)→ e − +(A,Z)

• 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

物質・生命科学 実験施設（MLF）

3GeV Rapid Cycling Synchrotron (RCS)

MLF H-Line

in production target

• 1. π production
• 2. µ production
• 3. muonic atom

formation

• 4. µ-e conversion

production target

proton π µ e J-PARC

DeeMe experiment

Pulsed proton beam from RCS

• Repetition 25Hz
• Fast extraction
• No residual protons in

kicker magnet off timing Pulsed proton 600ns 40ms

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No protons No protons

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DIO µ-e signal

After-Proton

Measurement

DeeMe experiment

The momentum distribution of µ-e electrons and backgrounds by Monte Carlo simulation

Decay In Orbit (DIO) = e- decayed from µ- in the muonic atom by µ− → e− +νe +νµ

• The signal electrons will be observed in delayed timing from pulsed proton.
• Measurement time is about 2µs.

Primary Proton Measurement

e- signals

= prompt burst +DIO electrons + µ-e signal 1µs 2µs

600ns 40ms

// //

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DeeMe experiment

After-Proton background

• If there are protons delayed from main pulse, they may hit the production target.
• Produced prompt burst → After-Proton background

Primary Proton Measurement

e- signals

= prompt burst +DIO electrons + µ-e signal

// //

After Proton

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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 µ-e signal

After-Proton

Measurement

The momentum distribution of µ-e electrons, DIO BG and After-Proton BG

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After-Proton counter

• Definition
• RAP < 10-18 will be required in DeeMe experiment
• According to a Monte Carlo simulation,

RAP = ———————— After-Protons Total protons To MLF / MR septum magnets

RCS ring Beam loss monitor(BLM)

proton beam

hitBLM × 40 = delayed protons ⇒ The BLM was set up in RCS tunnel RCS extraction region

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Fe absorber After-Proton counter

• The BLM had 2 scintillation counter and Fe absorber

Fe absorber (10cm thickness) scintillation counters particle efficiency 3GeV proton 0.98 Michel positron 0.04

AP解析‐清水宏祐

the time spectrum

It imply that there are some contamination by positrons decayed from the rest muons

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calculated by H. Shimizu

Analysis

It can be improved by suppression of the positrons

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New After-Proton counter

• 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

protons

Pb sci1 Pb sci2 Pb sci3 Pb

32mm 32mm

10mm 10mm 10mm

16mm 16mm

e+ e+

π µ

Beam Line

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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

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New counter with MLF trigger

TDC histograms coincidence TDC histogram

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

• f the counter.
• performance check with MR extraction trigger
• MR extraction
• trigger rate = ~1Hz
• extraction timing is not constant
• Difference between MR and MLF extraction
• the number of protons in a bunch
• emittance
• beam halo

waveform with MR trigger

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beam extraction timing

• TDC (3 counters coincidence)

MR extraction trigger

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Time distribution

Calculation of the suppression (New counter)

single counter coincidence

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f (x) = p0 ×exp(− t p1 )+ p2

Total hits = 2.811 x 105 Constant = p2 x 360 = 130.3 x 360

• exp. hits = 2.811 x 105 - 130.3 x 360 = 2.342 x 105

Total hits = 16 coincidence / single = 16 / 2.342 x 105 = 6.8 x 10-5

Calculation of the suppression (Fe absorber counter)

single counter coincidence

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f (x) = p0 ×exp(− t p1 )+ p2

Total hits = 1.269 x 105 Constant = p2 x 360 = 252.9 x 360

• exp. hits = 1.269 x 105 – 252.9 x 360 = 3.586x 104

Total hits = 51 coincidence / single = 51 / 3.586x 104 = 1.4 x 10-3

Calculation of the suppression

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New BLM Fe absorber BLM

coincidence / single = 1.4 x 10-3 coincidence / single = 6.8 x 10-5 The single PMT hit rates of each BLM are the same, the suppression of the new BLM looks increasing.

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

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