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Current status of MEG Experiment

Current status of MEG Experiment. Yasuko HISAMATSU ICEPP, The Univ. of Tokyo ICEPP Symposium. motivation for muegamma. mu e+ gamma. beyond SM SUSY-GUT promising. MEG Br 10^-14. MEGA(~1999) Br 1.2*10^-11. Background. muon radiative decay accidental background. e+ e-.

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Current status of MEG Experiment

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  1. Current status of MEG Experiment Yasuko HISAMATSU ICEPP, The Univ. of Tokyo ICEPP Symposium

  2. motivation for muegamma • mu e+ gamma • beyond SM • SUSY-GUT promising MEG Br 10^-14 MEGA(~1999) Br 1.2*10^-11 • Background • muon radiative decay • accidental background e+ e-

  3. The MEG collaboration ICEPP, University of TokyoY. Hisamatsu,T. Iwamoto,T. Mashimo, S. Mihara, T. Mori, H. Nishiguchi, W. Ootani, K. Ozone, T. Saeki, R. Sawada, S. Yamada, S. Yamashita KEK, TsukubaT. Haruyama, A. Maki, Y. Makida, A. Yamamoto, K. Yoshimura Osaka UniversityY. Kuno Waseda UniversityT. Doke, J. Kikuchi, S. Suzuki, K. Terasawa, A. Yamaguchi, T. Yoshimura INFN & Genova UniversityS. Dussoni, F. Gatti, D. Pergolesi, R. Valle INFN & Lecce UniversityS. Spagnolo, C. Chiri, P. Creti, M. Panareo, G. Palama’ INFN & Pavia UniversityA.de Bari, P. Cattaneo, G. Cecchet, G. Nardo’, M. Rossella INFN & Pisa UniversityA. Baldini, C. Bemporad, F.Cei, M.Grassi, F. Morsani, D. Nicolo’, R. Pazzi, F. Raffaelli, F. Sergiampietri, G. Signorelli INFN Roma I D. Zanello PSI, VilligenJ. Egger, P. Kettle, M. Hildebrandt, S. Ritt Budker Institute, NovosibirskL.M. Barkov, A.A. Grebenuk, D.G. Grigoriev, B, Khazin, N.M. Ryskulov

  4. MEG detector

  5. COBRA Magnet (Constant Bending Radius) Solenoid with a gradient field • Constant bending radius independent of emission angles -> Enable to sharply define the absolute momentum window of positrons • Low energy positrons quickly swept out -> Good pattern recognition and stable chamber operation

  6. Construction finished! Now @PSI Superconducting coil in cryostat. Compensation coil potentiometer Support frame

  7. On the axis Excitation Test Completed Successfully! • 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. Really graded!! Measured field Design field

  8. Liq. Xe calorimeter Detect scintillation light with 800 Liter liq.Xe and with 800 PMTs Liq. Xe • Uniform detector • High Light yield • Short decay time Minimize the pile-up of gamma event Design of liq.Xe calorimeter almost completed The start of the construction: 2004

  9. Large Prototype Stability of the detector, Study of cryogenics, absorption length, calibration method…

  10. Photon spectrum 129 MeV 54.9 82.9 Pi0 beam Test @PSI elementary process π-p→nγ E(γ)=129MeV π-p→π0 n π0(28MeV/c)→γγ Eγ γ θ θ γ 2 gamma rays emitted back to back in lab. frame: 55 & 84 MeV δEγ/Eγ < 1% θ<5° 5°=87mrad=8.7cm@1m

  11. Experimental Setup monochromatic γ beam the Energy Calibration 2γ from π0→2γ the absolute timing measurement

  12. Energy, Timing and Position Resolution Energy Resolution: 4.5% FWHM Timing Resolution: 100psec Sigma Position Resolution: 4.5~9.0 mm Expected Detector performance Energy Resolution: 1.4~2.0 %FWHM Timing Resolution: ~100psec FWHM Position Resolution: 4~16mm Q.E. improvement Wave form analysis Better resolution is expected

  13. PMT R&D Hamamatsu R9288 photocathode: K-Cs-Sb Aluminum strip Q.E. improved Hamamtsu R6041 photocathode: Rb-Cs-Sb Q.E. : ~10% Installed in Large Prototype

  14. Problem with old Type PMT UV 83MeV g Beam on off on BLUE 55MeV g The Deterioration of old type PMT output due to the high rate background. • Output from Al Strip Type PMT (new type) needs to be tested under the high rate background, 10^6 ~ 10^8 p.e. per sec

  15. PMT Test @ Univ. of Tokyo • Set up Liq. Xe PMT 5.5MeV alpha peak Alpha source(241Am ) LED PMT

  16. PMT Test Facility @Univ. of Tokyo Purification system Chamber Inside alpha source LED Xe tank Liq.Xe chamber PMT

  17. Condition and Procedure • alpha source : ~200Hz, • LED pulse height: 500p.e. ~ 12000p.e. per event • pulse shape: ~10nsec • rate: 100Hz ~ 10KHz • Trigger: alpha self trigger (veto by LED driver pulse) • Procedure • Pedestal Run & Gain calibration using LED • Alpha Run @ LED OFF • Alpha Run @ LED ON (LED : high rate background) • -Change LED Pulse height, rate and PMT gain • Investigate the cause of the change in PMT output • Breeder current ? • Deterioration of photocathode? Peak/Sigma (gain independent)

  18. 1*e6gain Result X: number of photoelectrons per second from LED Y: (peak/sigma @LED ON) / (peak/sigma @LED OFF) TB0094 TB0302 TB0568 TB0439 TB0102 TB0284 TB0268 TB0415 TB0239 Stable output up to 10^7p.e. !

  19. Summary Photon detector : Large prototype @PSI background estimation The construction start in 2004. COBRA magnet :Now @ PSI ! Installation & Engineering runs in piE5 PMT R&D : Problems with background in the beam area will be investigated this year. (Background measurement) 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.

  20. piE1 beam line @PSI Beam properties: Max. momentum: 280 [MeV/c] Solid angle 32[msr] Momentum acceptance 7.8% Momentum resolution 0.8 % π-flux: 8 * 105 /sec @ 1.6 mA Dipole Magnet Vertical & horizontal slits Graphite target Quadruple Magnet

  21. Result X: number of photoelectrons per second from LED Y: alpha peak (@LED ON) / alpha peak (@LED OFF) 1*e6gain TB0094 TB0302 TB0568 TB0102 TB0284 TB0439 TB0268 TB0415 TB0239 Yasuko HISAMATSU ICEPP Symposium @Hakuba February 2004

  22. Thermal neutron background estimation • Condition of the estimation • 16 n/cm^2/sec (MEG TN022) • From all direction • 6*10^5 photons ( : ~9MeV gamma ) are generated in LP MC 5.2 * 10^6 p.e. /PMT/sec @LP • Scaled to the final detector (surface area) 3.2 * 10^7 p.e./PMT/sec @final detector = 5.0 *10^-6 A @10^6gain

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