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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

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 ,

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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

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  1. 日本物理学会２００５年秋季大会　＠大阪市立大　２００５年９月１３日日本物理学会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-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

  2. Contents • Why waveform ? • Waveform data • Waveform simulation • Pile-up rejection • Summary 日本物理学会2005年秋季大会 　 @大阪市立大

  3. meg g background signal m menn + g e 52.8MeV g ? Photon yield • reject pile-up of g-rays m Crucial for the MEG experiment and very difficult without waveform image e Why use waveform data In the MEG experiment all PMTs are read by afast waveform digitizer • Using Lq.Xe as scintillator • large light yield • short decay time • short radiation length • Major background • Prompt background • Accidental background Unsegmented detector 日本物理学会2005年秋季大会 　 @大阪市立大

  4. Readout Shift Register Domino Circuit 10 channels x 1024 bins Waveform data Domino Ring Sampler (DRS) Developed by Stefan Ritt NIM A 518(2004) 470 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 2.5GHz sampling [mV] Xe waveform data were already taken successfully using prototype detector Data analysis is going on. I reported at last meeting... ~\10,000/chn [msec] 日本物理学会2005年秋季大会 　 @大阪市立大 Xe scintillation pulse

  5. Waveform simulation

  6. t= 45nsec electron a Waveform • Pulse shape is a consequence of various effects like, • Scintillation process • Light transport in the scintillator • PMT response • Shaping from circuit • Cables • Receiver (DRS) Xe scintillation process forg Decay time 45nsec PMT TTS 0.75nsec (Typ.) TTS : Transit time spread of PMT for individual photoelectrons 日本物理学会2005年秋季大会 　 @大阪市立大

  7. Waveform simulation • 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. 8000 p.e. • Shaped by low pass filter • RC shaping ( integration circuit ) • Time constant RC = 5 nsec • Data averaged pulse • Simulated pulse Simulated waveform is well fitted to real waveform. 日本物理学会2005年秋季大会 　 @大阪市立大

  8. Simulated waveform Now we can simulate waveform pulse by pulse. Pulse shapes are not constant especially for small pulses because of statistics. 2000p.e. 500p.e. 100p.e. Simulation Data width:height Distribution of pulse width Fluctuation of pulse shape is well simulated pulse width [nsec] Due to DRS response for small pulses We succeed in simulating pulse shape properly 日本物理学会2005年秋季大会 　 @大阪市立大 After this, use these simulated waveform for analysis pulse height [mV]

  9. Pile-up rejection

  10. g1 g2 Pile-up event Lq. Xe g1 • How to reject pile-ups ? • distribution of PMT output • pulse shape after DT g2 • DT = t2 – t1 • E1 + E2 = 1 (signal energy) # of p.e. 1 PMT output 2000p.e. + 1600p.e., DT = 20nsec 日本物理学会2005年秋季大会 　 @大阪市立大 0.8 + 0.2

  11. Pile-up rejection How to find pile-ups ? Peak search method simplest way but powerful in case of large DT Take moving average and count peaks DT=75ns, 2000p.e + 400p.e. Differential method powerful in case of DT around rise time Take differentiation and count its peaks Set threshold in peak finding with miss-rejection of non-pileup signal < 0.05% DT=15ns, 600p.e. + 1600p.e 日本物理学会2005年秋季大会 　 @大阪市立大

  12. Pile-up rejection • Difficult 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 small • Noise such as microstructure in pulse shape for small signal • Take sum of PMT outputs • Larger pulse • Microstructure in pulse shape • disappear Sum of all PMTs for signal g 日本物理学会2005年秋季大会 　 @大阪市立大

  13. 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% 40 130 # of PMTs # of PMTs S/N can be improved considerably 日本物理学会2005年秋季大会 　 @大阪市立大

  14. Rejection efficiency optimization E1 + E2 = 1 (signal) 日本物理学会2005年秋季大会 　 @大阪市立大

  15. Rejection efficiency 60% DT 8ns DT 50ns DT 100ns DT 10ns • Weak point • DT less than 10nsec • Small pulse after large one DT 15ns 日本物理学会2005年秋季大会 　 @大阪市立大

  16. Summary • We Succeed in simulating waveform from 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 , Eg: >5MeV, DT: >10ns 日本物理学会2005年秋季大会 　 @大阪市立大

  17. Next step • Rejection spatially separated pile-up using distribution of PMT outputs • Rejection efficiency against mg e g background 日本物理学会2005年秋季大会 　 @大阪市立大

  18. End of slides

  19. DRS principle 0.2-2 ns Inverter “Domino” chain IN Waveform stored Out FADC 40MHz Shift Register Clk “Time stretcher” GHz  MHz 日本物理学会2005年秋季大会 　 @大阪市立大

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