1. MEG 実験用液体 Xe scintillation detector の 40MeV γ 線を用いた性能評価 II 東大素セ、早大理工総研 B 、阪大理 C 、高エ研 D 、 BINP-Novosibirsk E, INFN-PISA F, PSI G 岩本敏幸、大谷航、小曽根健嗣、菊池順 B 、 久野良孝 C 、澤田龍、鈴木聡 B 、寺沢和洋 B 、道家忠義 B 、西口創、 服部紘二 B 、春山富義 D 、真木晶弘 D 、真下哲郎、三原智、 森俊則、八島純 D 、山口敦史 B 、山下了、 山下雅樹 B 、山田秀衛、吉村浩司 D 、吉村剛史 B 、 A.A.Grebenuk E, D.Grigoriev E I.Ioudine E, D.Nicolo F, S.Ritt G, G.Signorelli F 東京大学 久松康子 2003 年 9 月 12 日 日本物理学会秋季大会

2. The current status and schedule of MEG experiment Development of MEG Experiment Detectors ＊ Gamma beam test @PSI ＊ Liq. Xe Calorimeter -Filler study for the Liq. Xe calorimeter ＊ COBRA Magnet Schedule of MEG experiment Summary Outline 東大素セ、早大理工総研 B 、阪大理 C 、高エ研 D 、 BINP-Novosibirsk E, INFN-PISA F, PSI G 久松康子、岩本敏幸、大谷航、小曽根健嗣、菊池順 B 、 久野良孝 C 、澤田龍、鈴木聡 B 、寺沢和洋 B 、道家忠義 B 、西口創、 服部紘二 B 、春山富義 D 、真木晶弘 D 、真下哲郎、三原智、 森俊則、八島純 D 、山口敦史 B 、山下了、山本明 D 、槙田康弘 D 、 山下雅樹 B 、山田秀衛、吉村浩司 D 、吉村剛史 B 、 A.A.Grebenuk E, D.Grigoriev E I.Ioudine E, D.Nicolo F, S.Ritt G, G.Signorelli F

3. Development of MEG Detectors

4. Gamma beam test @ PSI Beam test using the monochromatic gamma beam at PSI πE1 beam line. *monochromatic γ beam the Energy Calibration *2γ from the reaction: π0→2γ the absolute timing measurement ＊ π - p→π 0 n π 0 (28MeV/c)→γγ ＊ π - p→nγ E(γ)=129MeV

5. kinematics θ γ γ EγEγ θ 2 gamma rays emitted back to back in lab. frame: 55 & 84 MeV δE γ /E γ < 1% θ<5° 5°=87mrad=8.7cm@1m

6. piE1 beam line @ PSI Beam properties: Max. momentum: 280 [MeV/c] Solid angle 32[msr] Momentum acceptance 7.8% Momentum resolution 0.8 % Graphite target Quadruple Magnet Dipole Magnet π-flux: 8 * 10 5 /sec @ 1.6 mA expected Vertical & horizontal slits

7. Experimental Setup  - - beam AT NaI Timing Counter target degrader counter Veto counter Trigger : coincidence 2 Counters & Timing counter & Liq.Xe Liq. Xe

8. Experimental Setup Cont’d Target NaI Timing Counter Liq. H 2 target Target cell: 41mm dia. 103mm length 64bars NaI (assembled to form an 8×8array) 63.5×63.5×406 mm 3 Position resolution (radial) : σr=4.8 cm @100MeV Installed in front of NaI detector 2plastic scintillators over lapped (5×5cm 2 ) Lead plate (6mm thick)

9. Prospects γ beam from π 0 →2γ will be used to calibrate the Liq. Xe calorimeter in MEG experiment @ piE5, PSI Resolution required in MEG experiment Beam Time : Sep. 24th to Dec. 10th

10. MEG experiment detectors Liq. Xe calorimeter Design of liq.Xe calorimeter has almost completed. The start of the construction: 2004 Subjects to be solved: Stress, Deformation, Heat Load, Need of filler

11. Filler study for the Liq.Xe detector Some incident photons lose their energy in Liq.Xe, which fills space between the detector wall and PMTs. To fill the space with materials of long radiation length (“Filler”) will improve the efficiency of this detector. Liq.Xe γ PMT PMT cover (acrylic) vacuum Signal cable PMT holder (G10) Honeycomb (SUS314) Incident window

12. Filler study Requirement for Filler: Long radiation length Do not contaminate liq.Xe The same expansion coefficient as the glass used in Stem A mixture of Epoxy resin and glass. Filler is attached directly to the PMT.

13. Cooling Test PMT heater PMTs with Filler are cooled down to 150K. The temperature of PMT is controlled by Liq.N2, a cold finger (Cu pipe) and a heater.

14. Now studying… The difference between the thermal expansion rate of epoxy resin and of SUS. Stress on the PMT cover

15. COBRA Magnet Superconducting coil in cryostat. potentiometer Support frame Compensation coil COBRA Magnet: Solenoid magnet for positron spectrometer Gradient field for high rate events Construction finished!

16. Final Excitation Test completed. ＊ Magnetic field inside the SC was measured. →Good Agreement with the calculation! ＊ Fringe field around the photon detector region was measured. →Suppressed by compensation coils. On the axis

17. The Schedule of MEG experiment Photon detector : Large prototype @PSIbackground estimation The construction start in 2004. COBRA magnet : Shipping to PSI on Sep. 26th Installation & Engineering runs in piE5 Beam line : Ready by the spring of 2004 Positron tracker : The construction start in 2004. Electronics & DAQ system : Start assembling in 2004. All the detectors will be installed in piE5 beam line by 2005. Engineering runs will start in 2005. MEG experiment starts at the beginning of 2006.

18. Summary Beam test using monochromatic gamma beam starts on Oct. 2nd. The design of the photon detector has almost completed and now studying details. (Filler problems and so on) The construction of COBRA Magnet has finished. (Good performance! ) Engineering runs will start in 2005, and MEG experiment at the beginning of 2006.