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 2004年度低温 学・超伝導学会 ＠八戸 業大学

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 2004年度低温 学・超伝導学会 ＠八戸 業大学

Photomultiplier (PMT) • Highly sensitive light sensor often used in high energy physics experiments • Electron tube device which converts light into a measurable electric current photon Electrode and dynode e- Photoelectric effect photocathode e- e. Electron collection and multiplication Measureable electric pulse 久松康子 2004年度低温 学・超伝導学会 ＠八戸 業大学

MEG Liq. Xe γ detector Detect scintillation light with 800 Liter liq. Xe and with 830 PMTs Liq. Xe γ PMT γ 久松康子 2004年度低温 学・超伝導学会 ＠八戸 業大学

PMT @ 165 K (Liq. Xe temp. ) photon photocathode e- Temperature surface resistance Quantum Efficiency Signal Output Need to reduce surface resistance of photocathode 久松康子 2004年度低温 学・超伝導学会 ＠八戸 業大学

PMT @165 K under high rate B. G. Background PMT signal output ~ 20 min signal PMT will be exposed to large amount of light produced by high rate background radiation PMT output needs to be stable under high rate B. G. expected ~20% B. G. ON time First version PMTs output deteriorates under high rate B. G. Related to the characteristics of photocathode at the low temperature 久松康子 2004年度低温 学・超伝導学会 ＠八戸 業大学

Development of PMT for MEG Experiment ØEfficient Q. E. @ 165 K (reduction of surface resistance) ØStable output under high rate background First Ver. Rb-Cs-Sb Second Ver. K-Cs-Sb Material to reduce surface R Mn layer Q. E. @ 165 K ~5% How much has Al Q. E. improved? Al Strip (doubled) Will PMT survive the high rate background environment ? ? ? @165 K ? Photocathode Final Ver. K-Cs-Sb 久松康子 2004年度低温 学・超伝導学会 ＠八戸 業大学

PMT Test @ Univ. of Tokyo Liq. Xe chamber 65 mm Pulse tube refrigerator Liq. N 2 AISIN PR 121 Compressor : TAC 101 J Cooling Power : ~25 W @165 K Liq. N 2 cooling pipe Cold head temperature monitor : Pt 100 Vacuume Platinum Thin Film Resistance Cold head temperature control : MINCO Thermofoil Heater Liq. Xe 久松康子 2004年度低温 学・超伝導学会 ＠八戸 業大学

PMT Test Set up Q. E. measurement ØHow much has Q. E. improved? Observe 5. 5 Me. V alpha event Gain calibration using LED Reference PMT 55 mm Gain : 106 241 Am (alpha source) LED 55 mm 46 mm PMT 33 mm 久松康子 2004年度低温 学・超伝導学会 ＠八戸 業大学

PMT Test Set up Rate dependence test ØWill PMT survive the high B. G. environment at 165 K? Pulse tube refrigerator Background signal Liq. Xe 241 Am (alpha source) LED PMT How to simulate High rate B. G. ? LED 久松康子 2004年度低温 学・超伝導学会 ＠八戸 業大学

Rate Dependence Test Procedure Liq. Xe 241 Am LED • simulate the high rate background • pulse height: 4000~7200 p. e. /event • pulse shape: ~10 nsec • rate: 500 Hz ~ 10 KHz 241 Am (alpha source) LED PMT alpha Observe 5. 5 Me. V alpha event, ~200 Hz 久松康子 2004年度低温 学・超伝導学会 ＠八戸 業大学

PMT for MEG final version signal output Rate Dependence @ Liq. Xe ~ expected 20 min PMT was tested under various background ~20% environment by changing the rate of LED B. G. ON time c. f. First Version PMT signal output 20 min B. G. ON The output from final version PMT is stable under the high rate background environment time Max. B. G. Level in MEG experiment 1. 3*107 p. e. /sec 久松康子 2004年度低温 学・超伝導学会 ＠八戸 業大学

Summary Ø PMT for MEG experiment has been developed. ØAble to operate under 165 K, Liq. Xe temp. Ø Cryogenic performance of Final Version PMT is tested @ liq. Xe. Ø PMT has efficient Q. E. even at 165 K Ø PMT output at 165 K is stable under the high rate background environment. 久松康子 2004年度低温 学・超伝導学会 ＠八戸 業大学

PMT for MEG Experiment Metal Cover SUS Able to withstand pressure up to 0. 3 MPa Photocathode : Bialkali Sensitive to VUV Window : Quartz glass Kovar Glass Kovar Metal 久松康子 2004年度低温 学・超伝導学会 ＠八戸 業大学

PMT Test facility @ Univ. of Tokyo Purification system Xe tank Liq. Xe chamber

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

Major Background for PMT Ømuon radiative decay ØGamma from positron annihilation ØNeutrons from proton beam π –p π0 n π0 γ γ 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 2004年度低温 学・超伝導学会 ＠八戸 業大学

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