meg 実験用液体キセノン検出器におけるデジタル波形処理を用いた...
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日本物理学会2005年秋季大会 @大阪市立大 2005年9月13日. MEG 実験用液体キセノン検出器におけるデジタル波形処理を用いた パイルアップ事象の研究. 東大素粒子セ , 早大理工総研 A , 高エネ研 B , BINP-Novosibirsk C , INFN-Pisa D , PSI E 岩本敏幸 , 内山雄祐 , 大谷航 , 小曽根健嗣 , 笠見勝祐 B , 菊池順 A , 澤田龍 , 鈴木聡 A , 寺沢和洋 A , 名取寛顕 , 西口創 , 春山富義 B , - PowerPoint PPT PresentationTRANSCRIPT
MEGMEG 実験用液体キセノン検出器における実験用液体キセノン検出器におけるデジタル波形処理を用いたデジタル波形処理を用いた
パイルアップ事象の研究パイルアップ事象の研究
東大素粒子セ , 早大理工総研 A, 高エネ研 B, BINP-NovosibirskC, INFN-PisaD, PSIE
岩本敏幸 , 内山雄祐 , 大谷航 , 小曽根健嗣 , 笠見勝祐 B, 菊池順 A, 澤田龍 , 鈴木聡 A, 寺沢和洋 A, 名取寛顕 , 西口創 , 春山富義 B,
久松康子 , 真木晶弘 B, 三原智 , 森俊則 , 山下了 , 山田秀衛 , A.A.GrebenukC, D.GrigorievC, Y.YuriC, D.NicoloD, S.RittE, G.SignorelliE
内山 雄祐内山 雄祐
日本物理学会2005年秋季大会 @大阪市立大 2005年9月13日
13/Sep/2005 日本物理学会2005年秋季大会 @大阪市立大
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Contents • Why waveform ?
• Waveform data
• Waveform simulation
• Pile-up rejection
• Summary
13/Sep/2005 日本物理学会2005年秋季大会 @大阪市立大
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Using Lq.Xe as scintillator• large light yield• short decay time• short radiation length
In the MEG experimentall PMTs are read by
a fast waveform digitizer
Major background• Prompt background• Accidental background
e
e
e
e
?
signal background
52.8MeV
Why use waveform data
Unsegmented detector
Photon yield
reject pile-up of -rays
Crucial for the MEG experiment and very difficult without
waveform image
13/Sep/2005 日本物理学会2005年秋季大会 @大阪市立大
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Waveform data
Analog sampling chip, switching capacitor circuits• Max sampling speed 4.5GHz (required 2.5GHz)• Sampling cells 1024• 8 data ch, 2 calibration ch(voltage and time) / chip• Read out speed 40MHz, 12bits• Domino wave runs continuously, only stopped by
the trigger
~\10,000/chn
DominoCircuit
ReadoutShift
Register
10 channels x 1024 bins
Developed by Stefan Ritt NIM A 518(2004) 470
Domino Ring Sampler (DRSDRS)
Xe scintillation pulse
Xe waveform data were already taken successfully using prototype detector
Data analysis is going on.
I reported at last meeting... [m
V]
[sec]
2.5GHz sampling
Waveform simulation
13/Sep/2005 日本物理学会2005年秋季大会 @大阪市立大
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WaveformPulse shape is a consequence of various effects like,
Scintillation process Light transport in the scintillator PMT response Shaping from circuit Cables Receiver (DRS)
electron= 45nsec
Xe scintillation process for Decay time 45nsec
TTS : Transit time spread of PMTfor individual photoelectrons
PMT TTS 0.75nsec (Typ.)
13/Sep/2005 日本物理学会2005年秋季大会 @大阪市立大
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Waveform simulation1. Sum up single electron pulses for all photoelectrons
• Single electron response spread by TTS (Gaussian).• Arrival time of each scintillation photon tracked by MC simulation.
2. Shaped by low pass filter• RC shaping ( integration circuit )• Time constant RC = 5 nsec
8000 p.e.
–Data averaged pulse–Simulated pulse
Simulated waveform is well fitted to real waveform.
13/Sep/2005 日本物理学会2005年秋季大会 @大阪市立大
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Simulated waveformNow we can simulate waveform pulse by pulse.
Distribution of pulse width
Fluctuation of pulse shape is well
simulated
2000p.e. 500p.e. 100p.e.
Pulse shapes are not constant especially for small
pulses because of statistics.pu
lse
wid
th [
nsec
]
Data width:height
pulse height [mV]
Simulation
Due to DRS response for small pulses
We succeed in simulating pulse shape properly
After this, use these simulated waveform for analysis
Pile-up rejection
13/Sep/2005 日本物理学会2005年秋季大会 @大阪市立大
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Pile-up event
12
1 PMT output2000p.e. + 1600p.e., T = 20nsec
1
2
Lq. Xe
after T
How to reject pile-ups ? distribution of PMT
output pulse shape
# of
p.e
.
T = t2 – t1 E1 + E2 = 1 (signal energy)
0.8 + 0.2
13/Sep/2005 日本物理学会2005年秋季大会 @大阪市立大
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Pile-up rejectionHow to find pile-ups ?
Peak search method simplest way but powerful in case of large T
Differential method powerful in case of T around rise time
Take moving average and count peaks
T=75ns, 2000p.e + 400p.e.
T=15ns, 600p.e. + 1600p.e
Take differentiation and count its peaks
Set threshold in peak finding with miss-
rejection of non-pileup signal
< 0.05%
13/Sep/2005 日本物理学会2005年秋季大会 @大阪市立大
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Pile-up rejectionDifficult to find pile-up by looking at individual PMT output.
• # of photons for each PMT is small• # of PMTs which can observe event as a pulse is smal
l• Noise such as microstructure in pulse shape for small s
ignal
Take sum of PMT outputs• Larger pulse• Microstructure in pulse shape
disappear
Sum of all PMTs for signal
13/Sep/2005 日本物理学会2005年秋季大会 @大阪市立大
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Pile-up rejection• Taking all PMTs sum is not good from S/N viewpoint. • Sum in order of PMT output• How many PMTs to be summed ?
70% 90%
40 # of PMTs
S/N can be improved considerably
# of PMTs130
13/Sep/2005 日本物理学会2005年秋季大会 @大阪市立大
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Rejection efficiency
optimization
E 1 + E 2
= 1 (signal)
13/Sep/2005 日本物理学会2005年秋季大会 @大阪市立大
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Rejection efficiency
T 8ns
T 10ns
T 15ns
T 50ns
T 100ns
60%
Weak point• T less than 10nsec• Small pulse after large one
13/Sep/2005 日本物理学会2005年秋季大会 @大阪市立大
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Summary• We Succeed in simulating waveform fr
om LXe detector.
• It indicates the detector response is well understood.
• Algorithm for pile-up rejection is studied and is being optimized.
• Pile-ups can be separated if ,E: >5MeV, T: >10ns
13/Sep/2005 日本物理学会2005年秋季大会 @大阪市立大
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Next step• Rejection spatially separated pile-up
using distribution of PMT outputs
• Rejection efficiency against
e background
End of slides
13/Sep/2005 日本物理学会2005年秋季大会 @大阪市立大
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DRS principle
Shift RegisterClk
IN
Out
“Time stretcher” GHz MHz“Time stretcher” GHz MHz
Waveform stored
Inverter “Domino” chain0.2-2 ns
FADC 40MHz