Abstract About MEG Experiment PMT for MEG photon
Abstract Ø About MEG Experiment Ø PMT for MEG photon detector Ø Works on Final Design of PMT Ø PMT test at Univ. of Tokyo Ø Summary 久松康子 日本物理学会 2004年秋季大会 @高知大学
MEG Experiment 52. 8 Me. V µ+ e+ γ Øbeyond SM 52. 8 Me. V ØSUSY-GUT promising MEGA(~1999) Br 1. 2*10 -11 MEG Br 10 -14 ØApproved by Paul Scherrer Institut ØUsing intense muon beam @PSI 1*108/sec ØStart of Physics Run : 2006 久松康子 日本物理学会 2004年秋季大会 @高知大学
MEG Liq. Xe γ detector Detect scintillation light with 800 Liter liq. Xe and with 830 PMTs PMT for liq. Xe detector needs to be/have… γ ØShort ØAble to operate under magnetic field Metal Channel Dynode ØDo not contaminate Xe ØAble to stand high pressure; up to 0. 3 MPa Metal Cover Positive HV Parts on Bleeder Circuit ØSensitive to VUV (Liq. Xe scintillation light) ØGood performance at 165 K (Liq. Xe temperature) ØStable under high rate background 久松康子 日本物理学会 2004年秋季大会 @高知大学
PMT performance @165 K Temperature surface resistance of photocathode Quantum Efficiency Photocathode Material to reduce surface R Q. E. @ 165 K Gain control First Ver. Rb-Cs-Sb Mn layer ~6% Difficult Second Ver. K-Cs-Sb Al Strip ? Easy 久松康子 日本物理学会 2004年秋季大会 @高知大学
Major Background for PMT Ømuon radiative decay ØGamma from positron annihilation ØNeutrons from proton beam π –p π0 n π0 γ γ T. Iwamoto, 27 a. SB-6 π –p Øneutrons from pion’s CEX reaction (@calibration run) c. f. muegamma event 52. 8 Me. V 55 nγ 83 129[Me. V] γ energy spectrum BG level ~ 2μA @106 gain (~107 p. e. /sec) 久松康子 日本物理学会 2004年秋季大会 @高知大学
PMT performance under high rate B. G. δG/G Ø Base Circuit for MEG PMT Gain fluctuation due to high rate background # of photoelectron per sec
PMT performance under high rate B. G. • Output from some First version PMTs deteriorates under high rate background. signal output ~20% Related to the characteristics of photocathode in the low temperature ØRb-Cs-Sb + Mn Layer @ First version PMT ØTo obtain “higher” gain, added more alkali ØLarger fraction of alkali changed the characteristics of photocathode PMT outputs deterioration from two reasons: τ~6 min B. G. ON Event # B. G. OFF due to photocathode Gain Variation due to base circuit A. Yamaguchi 29 a. SB-4 B. G. ON 久松康子 日本物理学会 2004年秋季大会 @高知大学
PMT for MEG First Ver. Second Ver. Final Ver. Photocathode Rb-Cs-Sb K-Cs-Sb Material to reduce surface R Mn layer Al Strip (doubled) Gain controll Difficult Easy Q. E. @ 165 K ~6% ? ? ? 久松康子 日本物理学会 2004年秋季大会 @高知大学
PMT Test @ Univ. of Tokyo Ø How much has Q. E. improved? Ø Will PMT survive the high background environment? low temperature effect on photocathode bleeder circuit current A. Yamaguchi PMT Test facility @Univ. of Tokyo Purification system Xe tank 久松康子 日本物理学会 2004年秋季大会 @高知大学 Liq. Xe chamber
PMT Test Set up Q. E. measurement Pulse tube refrigerator Observe 5. 5 Me. V alpha event Gain calibration using LED Reference PMT 241 Am 55 mm (alpha source) LED 55 mm g: gain c: ADC least count σ: standard deviation M: mean of ADC spectrum e: elementary electric charge Gain : 106 PMT Liq. Xe 久松康子 日本物理学会 2004年秋季大会 @高知大学
PMT Test Set up Rate dependence test LED • simulate the high rate background 241 Am • pulse height: 4000~7200 p. e. /event (alpha source) • pulse shape: ~10 nsec • rate: 500 Hz ~ 10 KHz LED Background Level Upper limit : 2µA, 1*107 p. e. /sec Pulse tube refrigerator Liq. Xe PMT alpha Observe 5. 5 Me. V alpha event, ~200 Hz 久松康子 日本物理学会 2004年秋季大会 @高知大学
PMT for MEG final version signal output Background Level Upper limit : 2µA, 1*107 p. e. /sec ~20% τ~6 min B. G. ON B. G. OFF Rate Dependence @ Liq. Xe Event # c. f. First Version PMT signal output Background 0. 34μA : 2. 0*106 p. e. /sec 1. 2μA 7. 2*106 p. e. /sec 2. 2µA Event # 1. 3*107 p. e. /sec 久松康子 日本物理学会 2004年秋季大会 @高知大学
Summary Ø Works on Final Design of PMT have finished, Adopting new photocathode material: K-Cs-Sb Adding Al Strip Pattern : reduction of surface resistance Ø Final Version of PMT is tested @ liq. Xe. Ø New photocathode mentioned above works quite well; Ø Q. E. is expected to be ~4 times bigger than that of R 6041 Q. Ø Stable output under the estimated background level in MEG 久松康子 日本物理学会 2004年秋季大会 @高知大学
PMT stability, DAQ Procedure DAQ started after all chamber components become low temperature Trigger : alpha self trigger DAQ Procedure : Pedestal Run Gain Calibration alpha run 久松康子 日本物理学会 2004年秋季大会 @高知大学
Condition and Procedure • Gain 1*106 • Trigger: alpha self trigger (veto by LED driver pulse) • Procedure Pedestal Run & Gain calibration using LED Alpha Run @ LED OFF 20 min Alpha Run @ LED ON 20 min -Change LED Pulse height, rate 久松康子 日本物理学会 2004年秋季大会 @高知大学
0 p Beam Test at PSI g p- (at rest) + p -> p 0 + n, p 0(28 Me. V/c) -> g + g (54. 9 Me. V<Eg<82. 9 Me. V) Almost monochromatic g g Opening angle 170° 175° 80 54. 9 Me. V Energy (Me. V) 82. 9 Me. V 55 p- + p -> n(8. 9 Me. V) + g (129 Me. V) linearity check 55, 83 and 129 Me. V neutron response p 0 155 Opening angle(deg) 180 55 80 Energy (Me. V)
Radiative Capture events in Xe 133 Xe 132 Xe 131 Xe 135 Xe 137 Xe 129 Xe + n -> 130 Xe + g etc… Many g’s are emitted, not one. 130 Xe
g from radiative muon decay 108 m/s->106 menng/s acceptance 10% Mean deposit energy 5 Me. V 1 photon = 24 e. V Xe detector front face 200 PMTs, QE 10%, coverage 50%, photon collection 50% • 106 mgx 0. 1 x 5 x 106 Me. Vx 0. 1 x 106 x 10 -19 Cx 0. 5/24 e. V/200 PMTs = 0. 4 m. A • • •
Inelastic reaction of different nuclei in Xe 126 Xe 124 Xe 129 Xe 130 Xe 132 Xe 0 Me. V 134 Xe 15 Me. V 128 Xe 131 Xe 136 Xe There are edges for different Xe nuclei around 9 Me. V.
CRYOGENIC OPERATION FOR LARGE-PROTO DETECTOR -Heat Load- *Static heat load depends on manufacturers design *PMT power dissipation 65 m. W/PMT *Due to number and length of cables
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