1. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Contents 1. MEG experiment 2. LXe Purification 3. Prototype Performance 4. Expected Performance 5. Toward the MEG experiment 6. Summary Liquid Xenon Scintillation Detector for the New   ｅ  Search Experiment Kenji Ozone （ ICEPP, Univ. of Tokyo, Japan ）

2. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Physics Motivation and event signature SU(5) SUSY  LFV process  Forbidden in the SM  Sensitive to the new physics such as SUSY-GUT, SUSY-seesaw etc.  Our goal : Br(  ->e  )>10 -13 ~10 -14 Present limit < 1.2x10 -11 (MEGA) Clear 2-body kinematics  E e = E  = 52.8 MeV  Back to back event  Time coincidence

3. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 MEG Detector LXe scintillation detector Drift chamber Timing Counter Compensation Coil COBRA Magnet Surface  beam 262cm 252cm  Initial goal at 10 -13, finally to 10 -14

4. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Signal and backgrounds   +  e +  signal –Back to Back –E e =E  =52.8MeV  Two major Backgrounds –Accidental overlap  e +  from Michel decay   from radiative decay, e + -annihilation in flight Down to ～ 10 -14 –Radiative  + decay Down to <10 -14  e  e  e  ?

5. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Polarized muon beam Muons from “Surface” of  + production target  + decay at rest near the surface Primary Proton  + stop  p   29.8MeV/c  100% polarized  + /e + separator MEG detector Primary Proton Quadruple magnets Beam Transport Solenoid Bending magnets Degrader  E5 area @PSI  + Beamline target

6. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 COBRA spectrometer COBRA magnet was already installed into the  E5 area in PSI. Constant bending radius independent of the emission angle e + momentum easily used at trigger level Michel positrons are quickly swept out reduce the hit rate for stable operation

7. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Gamma-ray detector in MEG detector The gamma-ray detector is a key detector in MEG experiment. Positron spectrometer can’t distinguish Michel positrons from ones of MEG event. Photon yield per decay Gamma-ray energy / 52.8MeV 1.0 10 -4 0.9 10 -6 On the other hand, 52.8-MeV gamma ray in gamma- ray detector is only MEG event.

8. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Why Xe ?  High density and High light yield 1 st conversion depth: 2 cm ~ 10 cm Wph: 21.7 eV (75% of NaI(Tl))  Good Energy, Position, Time resolutions  Fast Decay reduces pile-ups. τ(recombi.) = 45 nsec Low temperature: 165 K requires refrigerator and special PMT Wavelength: ~178 nm requires VUV-sensitive PMT Light absorption requires contaminant level of 100 ppb (water) T.Doke and K.Masuda, Nucl. Instr. And Meth.A420 (1999) 62.

9. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 LXe scintillation detector for the MEG experiment g Detector concepts Observe as many photoelectrons as possible with a great accuracy.  Many PMTs are directly immersed in LXe. Kamiokande-like detector.  Thin material on the incident face. Al honeycomb, compact PMT… 52.8MeV  800 liter liquid xenon  120 o, |cos  |<0.35, depth~50cm  830 PMTs 67cm Energy Total number of photons Timing Arrival time of photons Position Next page……

10. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Position reconstruction 52.8MeV  LXe  Position Reconstructed by outputs of 4PMTs ~ 10 PMTs Conversion position (X,Y) weighted mean in a region Conversion depth spread of distribution

11. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Prototype LXe detectors The strategy to develop LXe detector  10-liter prototype ( 2.34L eff. vol. ) verified the principle LXe detector  100-liter prototype ( 68.6L eff. vol. ) Theme of my doctoral thesis

12. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 100-liter prototype ■ 68.6-liter active volume ■ 228 PMTs ● a source ( 241 Am) x4 PMT calibration (QE measurement) Stability monitor ● LED x8 PMT calibration (gain adjustment) ● cosmic ray muon counter (3pairs) Light yield monitor 372mm X 372mm X 496mm

13. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 100-liter prototype Prototype LXe Scintillation Detector 1k liter LN2 tank Compresser for refrigerator Xe line Student A window ＫＥＫ east counter hall π ２ area 2002 Spring Student B

14. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Purpose of 100-liter prototype Construction of a larger prototype of LXe scintillation detector Never constructed such a large detector. Test for detector components PMTs, feed-through connectors, Cryostat, PMT holder, DAQ, Slow-control system, Purification system, … long-term stable operation Pulse tube Refrigerator, monitoring of temperature and pressure Performance Test for higher energy gamma rays Resolutions of energy, time, and position for 40 MeV g

15. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 PMT (HAMAMATSU R6041Q) Features 2.5-mmt quartz window 2.5-mmt quartz window Q.E.: 6% in LXe (TYP) Q.E.: 6% in LXe (TYP) (includes collection efficiency) (includes collection efficiency) Collection eff.: 79% (TYP) Collection eff.: 79% (TYP) 3-atm withstanding pressure 3-atm withstanding pressure Gain: 10 6 (900V supplied TYP) Gain: 10 6 (900V supplied TYP) Metal Channel Dynode thin and compact Metal Channel Dynode thin and compact TTS: 750 psec (TYP) TTS: 750 psec (TYP) Works stably within a fluctuation of 0.5 % at 165K Works stably within a fluctuation of 0.5 % at 165K 57 mm 32 mm

16. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Gain adjustment with LEDs  Assume the LED output obeys Poisson distribution.  The PMT outputs according to the LED intensity. LED 200fC/ch: charge,electron elementary: gain,:  c q g spectrum, LED ofMean : spectrum, LED ofMean: spectrum, pedestal ofdeviation: spectrum, LED ofdeviation: 0 0 M M  

17. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Q.E. estimation with a particle data 1. Make MC samples for alpha particle events. (QE = 5.0% fixed) 2. Compare the measured data with MC. Example Data=MC*1.42 QE = 3.5%

18. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Light yield monitor by cosmic-ray muons Data from cosmic-ray muons is useful for monitoring higher light yield. The cosmic-ray events are triggered with three pairs of counters (7cm x 7cm) above and below the vessel.

19. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 LXe purification and Absorption length measurement At the early stage, LXe was contaminated…

20. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Water contamination In principle, Xe scintillation photons are not re-absorbed by xenon atoms. Possible contaminants: water oxygen

21. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Residual gas analysis H2OH2O O2O2 CO 2 CO, N 2 Xe H2H2 Residual gas after recovering xenon was analyzed with Q-mass spectrometer at room temperature.

22. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Purification system Purification : ~1200 hours flow rate = 5 liter/min (GXe)

23. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Growth of scintillation photon yield The light yield was increased for 600 hours. Far PMTs Near PMTs

24. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Growth of photon yield Npe~25000Npe~85000 a particle data Cosmic-ray m data Npe~300Npe~1400 Before After

25. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Absorption length estimation l abs is estimated to be 12.0±1.8 cm over 1m (90% C.L.) LXe data were compared with LXe MC samples( l sca ~∞). LXe(data)/MC Before After Before

26. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Other efforts for pure LXe  Replacement PMT cover: acrylic to Teflon Filler in incident face: Silicon rubber to stycast with glass Filler at the side of PMT holder: acrylic plate to SUS hollow box  Working environment open-air to clean-room  Circulating pump (not yet) gaseous pump to fluid pump

27. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Energy resolution expected for 52.8 MeV g MC(prototype) l sca =45cm If l abs is over 1m, s u /E ~ 1.2%. Energy distribution was obtained with PCA(principal component analysis) to be fitted with Gaussian with exponential tail. l abs =1m l sca 45cm FWHM uu Response function

28. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Performance test with 40MeV LCS beam Purpose For 10~40 MeV gamma rays - Energy resolution - Position resolution Evaluate performance for 52.8MeV gamma rays.

29. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 TERAS Beam Test @ AIST Incident g beam  Not monochromatic  Compton edge: 10, 20, 40MeV  collimator: 1 mm φ

30. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Experimental setup @ TERAS

31. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Experimental setup @ exp. room LCS beam

32. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Incident beam LCS beam

33. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Incident beam 10MeV 20MeV 40MeV Energy spread becomes narrow by the collimator and the sharpness of the Compton edge is kept. Energy resolution

34. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Energy Spectrum Depth parameter The spectrum has lower tail. The resolution is evaluated by upper sigma.

35. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Fitting Expected incident Compton spectrum Response function The spectra were fitted with a convolution of the response function and incident LCS spectrum.

36. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Energy Resolution at P0 & P9 (update) Depth parameter > 2.0 1.4% in  for 52.8MeV

37. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Red circle: (Sum of front outputs) / 2 Depth parameter; Nf := # of PMTs in Reconstructed (x,y); is weighted mean in Vertex Reconstruction depth=4.4cm depth=15.3cm Depth ~ spread of output distribution.

38. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Difference between true and reconstructed vertex  ~6mm MC Nf 1 st Conversion Depth depth (x, y)

39. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Event Selection & efficiency Nf(0.5)>2 67% P0

40. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Fitting Fitted with 2-D Double Gaussian F(x,y) = a(narrow Gaussian) + (1-a)(broad Gaussian), a: ratio

41. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Position Resolution at P0 & P9(update) ~90% ~10% 3.6~5.0mm (90%) in  8.0~11.1mm (10%) in   for 40 MeV  and for 52.8MeV

42. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Toward the MEG experiment

43. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Prototype to final design What’s the difference? Shape box -> C-shape checked by “Mask analysis” Data Q-integrated ADC, discriminator & TDC -> waveform digitizer Calibration

44. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Mask analysis –Switch off half of the PMTs in the front face Use 4x4 PMTs out of 6x6 PMTs –Switch off PMTs on the side walls  –Compton Edge shifts by 6.2% –Resolutions are almost same (1.84 to 1.85% in  ) before and after switching off. –1 plane off  2.05% in  –2 planes off  2.22% in  –3, 4 planes off  > 3% in 

45. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Waveform analysis & high QE PMT 2.5GHZ sampling Energy and timing resolution will be improved hopefully. In particular pile-up rejection power will be up. QE: 5% to 15% ave.

46. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Calibration in MEG experiment Absolute calibration Energy (once a week/month…) -  0 ->  decay Position - radiative muon decay Timing - radiative muon decay relative adjustment (daily) - wire alpha source, cosmic-ray muon

47. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Energy calibration with  0 decay  - (at rest) + p ->  0 + n,  0 (28MeV) ->  54.9MeV<E  <82.9MeV) Almost monochromatic  is available by selecting opening angle. 170°175° 54.9MeV 82.9MeV Opening angle(deg) Energy (MeV) 15518055 80 55 80 Energy (MeV) 0.3 MeV FWHM 1.3 MeV FWHM

48. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 test with  0 decay @ PSI  8x8 NaI array opposite to Large Prototype Xe detector to know opening angle each NaI is 6.3x6.3x40.6cm3  Liquid H 2 target

49. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Energy Resolution 4.5% FWHM Energy spectrum @ 54.9 MeV  This satisfies the requirement 5.0 4.0 3.0 2.0 1.0 Energy resolution in right  (%) preliminary TERAS data PSI data Right  is a good function of energy

50. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Proton beam: 1.8mA Pion Rate: 2x10 8  - /sec Collimate: 2PMTs x 2PMTs ~ 150cm 2 20  /sec # of PMTs on incident face: 216PMTs required: 30,000 evts/run takes 81,000sec~ 1day Energy Calibration Anti Counter up tilt down Support structure: straightly up and down Tilt mechanism at every height for NaI front to face target direction. target 0000   55, 83MeV

51. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Expected Performance

52. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Expected Performance Generate background events –Accidental overlap  e +  from Michel decay   from radiative decay, e + -annihilation in flight  Pile-ups –Radiative  + decay ff f  B acc ∝ δ E e ・ δ t e  ・ (δ E  ) 2 ・ (δ  e  ) 2 ・ N 

53. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 90 % C.L. Sensitivity 5.8x10 -14 4.5x10 7 Solid angle:  /4  =0.09 Positron detection efficiency:  e =0.90 Gamma detection efficiency:   =0.67 Event selection efficiency:  sel =0.7 Gamma energy resolution: 5.2% Gamma position resolution: 4mm-11mm Gamma timing resolution: 179 psec Positron energy resolution: 0.8% Positron timing resolution = 100 psec Positron position resolution = 10.5 mrad

54. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Decay Angular Measurement  Conditions:   + beam intensity : 4.5x10 7 /sec  beam time : 5.2x10 7 sec (2 years)  P  =97% (from MEGA) MEG search with sensitivity down to 10 -13 with depolarized μ+ beam Muon Stopping target: polyethylene Define the model of the new physics with polarized μ+ beam Muon Stopping target: graphite, Be, Al,…

55. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 SUSY models and Asymmetry  SU(5) SUSY-GUT A = +1 (A L  0, A R =0)  SO(10) SUSY-GUT A  0 (A L  A R )  MSSM with R A = -1 (A L =0, A R  0) Detector acceptance Y.Kuno et al., Phys.Rev.Lett. 77 (1996) 434 dN(  +  e +  ) / dcos  e  Br(  +  e +  )x(1+AP  cos  e )/2 Asymmetric Parameter;A = (|A L | 2 -|A R | 2 )/(|A L | 2 +|A R | 2 )

56. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Background distribution Radiative  + decay –N(  +  e +  ) ∝ (1+P  cos  e ) e + from Michel decay ∝ (1+P  cos  e ) from radiative decay ∝ (1+P  cos   ) Back to back :   =  e -  ⇒ Accidental B.G. ∝ (1-P   cos 2  e )  ～ 11% suppression @ P  =97%, cos  e =0.35 Detector acceptance

57. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 68%, 90%, 95% C.L. Sensitive Regions 68.3%90.0% 95.4% A=+1 B(  +  e +  ) = 10 -12 Poisson-distributed  2 =  [2(N obs -N exp )+N obs log e (N obs /N exp )] Assumptions

58. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Summary  We proposed a novel LXe scintillation detector for the MEG experiment.  A 100-liter detector was constructed to design the final detector.  The components such as monitoring system, PMTs, and, especially the cryostat, worked as expected.  We developed a purification technique and absorption length reached over 1m at 90 % C.L.  The detector performance was estimated to be  E /E=2%,  pos >4mm for 52.8 MeV in MEG experiment.  Sensitivity of MEG detector was estimated to be 5.8x10 -14 90%C.L.  The final detector was already designed, and is ready for construction toward the physics run in 2006.

59. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Reachable sensitivity by MEG experiment Physics run in 2006 5.8x10 -14 90% C.L.

60. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 End of Slides

61. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 PMT calibration Gain ∝ (HV) 9

62. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 LXe operation  Evacuating: ~10 days downs to an order of 10 -3 Pa.  Pre-cooling: 1 day The 0.2 MPa GXe in the inner vessel is cooled to 165 K in advance.  Liquefaction: 2 days Liquefied with LN 2 cooling pipe. GXe is purified before entering the vessel. The pressure is kept <0.13 MPa.  LXe-keeping: 2000 hours max. Mainly by refrigerator. By LN 2 if over 0.13 MPa.  Purification : ~1200 hours flow rate = 5 liter/min (GXe)  Recovery: 2 days Cool Xe tank storage with LN 2.  Warming-up: 3 days

63. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Dustbox The s E is evaluated to be ~1% from the extrapolation to 52.8 MeV. The s t is evaluated to be ~50 psec for 20,000 photoelectrons estimated from the result simulated for 52.8-MeV g. ● 8 LEDs inside PMT holder ● Scan HV to get gain curves for all PMTs

64. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 10-liter (small) prototype ● g sources ( 137 Cs, 51 Cr, 54 Mn, 88 Y) Resolution evaluation ● a source ( 241 Am) PMT calibration, stability check ● LED PMT calibration ■ 2.34-liter active volume ■ 32 PMTs Purpose First “Kamiokande”-like LXe detector Test for R6041Q in LXe and cryostat for LXe. Estimate of the performance for low energy g rays Energy, time, and position resolutions with < 1.8-MeV g sources. 116mmX116mmX 74mm

65. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Energy Resolution Fully-contained events in each energy distributions are fitted with an asymmetric Gaussian.

66. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Position Resolution PMTs are divided into two groups. γ int. positions are calculated in each group and then compared with each other. Events in the central 2cmX2cm area are selected. Position resolution is estimated as s z1-z2 /√2

67. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 PMTs are divided again into two groups. In each group the average of the time measured by TDC is calculated after slewing correction for each PMT. The time resolution is estimated by taking the difference between two groups. Resolution improves as ～ 1/√Npe FWHM<120 psec for 52.8 MeV g. Time Resolution

68. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 How much water contamination? data/MCSimulated data Before purification: ~10 ppm After purification: ~100 ppb

69. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会  Constructed the first LXe scintillation detector.  The resolutions are evaluated for low energy g. Energy: 4.2~9.4%, Position: 6.3 ~ 19 mm, Time: ~380 psec (FWHM) If extrapolated to 52.8-MeV, resolutions are be expected: energy; ~1%, position; a few mm, time;~100 psec (FWHM)  Stable operation for the cryostat. PMT output fluctuation: ~ 0.5 %. Summary on Small Prototype

70. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Absorption length estimation Comparing the two results, the absorption length is estimated to be over 3m (97.8% C.L.). Measured / MC(abs=inf.) MC(abs=var.) / MC(abs=inf.) measured a data/simulated a data simulated data

71. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Thickness of incidence face PATH A: 0.24 X 0 PATH B: 0.24 X 0 The Most of g -rays transmit to the LXe volume through the incident face.

72. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Energy Spectrum data MC

73. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Stability of PMT outputs The a particle data are useful for monitoring the stability of PMTs because it is regarded to be a point-like source. After the completion of the liquefaction, the PMT output is stabilized within 1.5 % in 50 hours. a ±1.5%

74. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Q.E. estimation with a particle data Compared with the simulated data, the a data in LXe can estimate Q.E.s, which include collection efficiencies of the PMTs.

75. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Position Resolution at P0 & P9 MC data

76. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Position Reconstruction depth=4.4cm depth=15.3cm q i : number of p.e. observed by i-th PMT Q f : Total number of p.e. observed by i-th PMT C i : Ratio of overlap of the red circle for i-th PMT Simple weighted mean Local weighted mean

77. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Position Resolution at P0 & P9(update) MCdata If the range of Nf(0.5) is from 2.0 to 20.0 and fitted with 2-D double Gaussian ~10% ~90% ~10%

78. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Position Fitting (old) Data; 40 MeV P0 Data; 40 MeV P9 Fitted with 2-D Gaussian

79. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 MC

80. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Event Selection Correction 4<Nf(0.5)<13

81. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Trigger

82. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Energy Resolution at P0 & P9 (old) MCdata

83. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Energy Resolution at P0 & P9 (update) MCdata 古い If the range of Nf(0.5) is from 2.0 to 20.0

84. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Fitting (old) Data; 40 MeV P0 Data; 40 MeV P9 Fitted with 2-D Gaussian

85. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Vertex Reconstruction depth=4.4cm depth=15.3cm q i : number of p.e. observed by i-th PMT Q f : Total number of p.e. observed by i-th PMT C i : Ratio of overlap of the red circle for i-th PMT Simple weighted mean Local weighted mean

86. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Sensitive Region for A=+1 Excluded region for each B(  +  e +  ) @ A=+1 68.3% 90.0% 95.4% excluded Allowed

87. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Mask analysis 1 –Switch off half of the PMTs in the front face Use 4x4 PMTs out of 6x6 PMTs –Switch off PMTs on the side walls 

88. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Mask analysis 2 Only 4x4 PMTs on the front face Switching off half the front PMTs –Compton Edge shifts by 6.2% –Resolutions are almost same (1.84 to 1.85% in  ) before and after switching off. Switching off PMTs on the side wall(s) –1 plane off  2.05% in  –2 planes off  2.22% in  –3, 4 planes off  > 3% in  4 planes off 3 planes off 2 planes off 1 plane off 1/N pe 1/sqrt(N pe ) Number of Photoelectrons

89. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Mask analysis 3 1 plane off 3 planes off Deterioration of the energy resolution when switching off PMTs is not mainly caused by loss of N pe. PMTs on the side walls compensate 1 st conversion point dependence. Number of Photoelectrons D D

90. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Mask analysis 4 All PMTs on:  =1.8% Switching off one PMT on the front wall. –the nearest PMT   =2.3% –2 nd nearest PMT   =1.9% –3 rd nearest PMT   =1.9% 300 PMTs on the front face in the final detector –~4/300 = 1.3% loss of acceptance F30 off  =2.3% F22 off  =1.9% F28 off  =1.9%

91. 27/Jan/2005 K. Ozone 2004 年度博士論文審査会 Pile-up rejection Pile-up rejection