, PSI A, UCI B, ETH C A, , , A, , , , , , , B, M.Schneebeli C, S.Ritt A MEG 27/Mar/2006 2006 2 Contents Introduction Performance estimation of MEG -ray detector Pile-up rejection Summary 27/Mar/2006 2006 3 Using Lq.Xe as scintillator large light yield short decay time short radiation length Major background Prompt background Accidental background e e e ee ? signal background 52.8MeV Background & waveform data Unsegmented detector limit this experiment Photon yield Pile-up photon yield Good resolution Pile-up rejection Crucial for the MEG experiment and very difficult without waveform image 27/Mar/2006 2006 4 Waveform data Developed by Stefan Ritt NIM A 518(2004) 470 DRS Domino Ring Sampler (DRS) Xe waveform data were already taken successfully using prototype detector Xe 2.5GHz sampling Analog sampling chip, switching capacitor circuits Max sampling speed 4.5GHz (required 2GHz) Sampling cells 1024 Read out speed ~40MHz, 12bits Domino wave runs continuously, only stopped by the trigger (role of analog pipeline) We have also already developed waveform simulation successfully. Xe scintillation pulse x10 -6 27/Mar/2006 2006 5 Waveform analysis Baseline Charge integration Constant fraction timing Pulse fitting using template Baseline, Charge, timing Chi-square Fast analysis 27/Mar/2006 2006 6 Performance Estimation of MEG -ray Detector using Waveform Simulation The first estimation Full simulation of the final detector Using waveform Uniform injection for active volume 27/Mar/2006 2006 7 Liq. Xe -ray detector Development view Cross section view For signal -ray(52.8MeV) charge from integration timing from template fitting ( fitting) Coordinate system 27/Mar/2006 2006 8 z =5.4mm v =4.8mm Position resolution w =6.6mm Depth Simple calculation of solid angle Fitting light distribution For energy deposit > 50MeV 27/Mar/2006 2006 9 Qsum after correction Depth corr. Energy reconstruction Sum of charge of all PMTs Weighted by density of PMT correction by position cut if depth < 2cm (efficiency 81%) High energy tail is crucial up =1.2% FWHM = 3.1% Cut events if one PMT observe more than 9000p.e. (efficiency 91%) Light is concentrated on one PMT 27/Mar/2006 2006 10 Depth correction. Time resolution Average of time of each PMT Weighted by square root of N p.e. N p.e. threshold Correction by depth Correction by position For energy deposit > 50MeV t =71psec X10 -9 Pile-up rejection 27/Mar/2006 2006 12 Pile-up event 1 PMT output 2000p.e p.e., T = 20nsec 11 22 Lq. Xe after T # of p.e. T = t 2 t 1 E 1 + E 2 = 1 (signal energy) 27/Mar/2006 2006 13 Pile-up Analysis Time separation Use time distribution of each PMT When gammas are away both in time & space. Waveform analysis When gammas are close spatially. Pattern recognition When gammas incident at the same time. Two gammas from AIF 27/Mar/2006 2006 14 Pile-up rejection by waveform T=50ns. T=15ns 11MeV + 42MeV Peak search method Differential method T 8ns T 10ns T 15ns T 50ns T 100ns Weak point T less than 10nsec Small pulse after large one Misidentification probability < 0.05% 27/Mar/2006 2006 15 3cm 4ns 10cm space 10ns 30ns Waveform time Ex. E1 + E2 = 27/Mar/2006 2006 16 Pile-up rejection by timing If time difference > 4nsec, then that event is pile-up event. Assume, Miss ID probability : 1.0% Maximum time difference between PMTs T = 8nsec Can close up to 3~4 nsec 27/Mar/2006 2006 17 3cm 4ns 10cm time space 10ns Waveform Timing 30ns Ex. E1 + E2 = 27/Mar/2006 2006 18 Pile-up rejection using 2 If 2/NDF > 2, then that event is pile-up event. Assume, Miss ID probability : 3.7% = 1 ( E1 + E2 = Esignal ) t = 10nsec Rejection efficiency : 72.3% Distance of two gamma < 20cm Maximum of ( 2/NDF ) Distance of two gamma 27/Mar/2006 2006 19 3cm 4ns 10cm time space 10ns Waveform Timing 30ns Ex. E1 + E2 = 27/Mar/2006 2006 20 3cm 4ns 10cm time space 10ns Waveform AIF Timing 30ns Ex. E1 + E2 = Photon Distribution Pile-up rejection using light distribution 27/Mar/2006 2006 21 Summary Performance estimation was done using simulated waveform Able to get performance estimated from prototype detector ( a bit worse) Large improvement in pile-up rejection Prototype beam test Simulation position4mm5mm energy1.3%1.2% timing65psec71psec (sigma) new geometry (C-shape) waveform data randomly injection 27/Mar/2006 2006 22 Summary It is important to develop the algorithm appropriate for the design of final detector Pile-up rejection by light distribution Preparation to analyze real data Data taking will start in this year End of slides 27/Mar/2006 2006 24 Physics motivation SU(5) SUSY-GUT SM Clear 2-body kinematics Ee = E = 52.8 MeV Back to back Time coincidence Lepton Flavor Violation minimal SM Sensitive to the new physics SUSY GUT SUSY seesaw, etc 27/Mar/2006 2006 25 MEG experiment Approved in 1999, at Paul Scherrer Institut Physics run in 2006 Initial goal at , finally to + beam : DC Beam 10 8 + /s detector : 800liter 850 PMTs e + detector : (COBRA) Drift chamber system Timing counter 27/Mar/2006 2006 26 DRS principle Shift Register Clk IN Out Time stretcher GHz MHz Waveform stored Inverter Domino chain ns FADC 40MHz 27/Mar/2006 2006 27 Error of pulse shape Basically consider the statistical error of photoelectrons. Have to take care of the correlation between point and point. Some kind of scale factor(like fano factor) E Estimated error Actual deviation data simulation Choose this factor from the effect of shaping of the system 27/Mar/2006 2006 28 Shower estimation Reconstruction of 1 st interaction point is affected by spread of shower Center of light would reflect the effect Zave - Zrec Zrec Z0 27/Mar/2006 2006 29 z =5.4mm v =4.8mm Position resolution Energy deposit > 50MeV 27/Mar/2006 2006 30 Depth reconstruction Depth parameter 2 Nf(0.5) Fit parameter d deep shallo w Fitting light distribution is suitable for the final detector 27/Mar/2006 2006 31 Energy resolution Event in high energy tail are seen when light is concentrated on one PMT Cut events if one PMT observe more than 9000p.e. (efficiency 91%) up =1.2% FWHM = 3.1% Total # of p.e. No events 27/Mar/2006 2006 32 Time resolution Shallow event High threshold for Np.e. Inner face only Deep event Low threshold Use all faces p.e. > 1100 PMT (inner face) p.e. > 100 PMT (all faces) # of PMTs used for timing 27/Mar/2006 2006 33 + PILE UP EVENTS (RD+RD dominant) Qsum spectrum Radiative decay AIF RD+RD (muon stop rate=E7) Reconstructed E Photon yield per muon decay # of Background events, 2 years RUN TOTAL RD AIF RD+RD Muon stopping rate [/sec] Reconstructed E Background 27/Mar/2006 2006 34 CL 90% Sensitivity BEAMTIME=4E7 sec 2 year YEAR MONTH BEAMTIME