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Wataru OOTANI International Center for Elementary Particle Physics University of Tokyo

Development of Liquid Xenon Photon Detector for μ → eγ Search Experiment at PSI μ → eγ 崩壊探索実験用液体キセノン検出器の開発. Wataru OOTANI International Center for Elementary Particle Physics University of Tokyo For the MEG collaboration. Introduction μ→eγSearch Experiment at PSI

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Wataru OOTANI International Center for Elementary Particle Physics University of Tokyo

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  1. Development of Liquid Xenon Photon Detector for μ→eγ Search Experiment at PSIμ→eγ崩壊探索実験用液体キセノン検出器の開発 Wataru OOTANI International Center for Elementary Particle Physics University of Tokyo For theMEG collaboration • Introduction • μ→eγSearch Experiment at PSI • Status of R&D of Liquid Xenon Detector • Summary

  2. MEG　collaboration （仮名） in Japan 東大素セ 浅井祥仁、大谷航、小曽根健嗣、佐伯学行、西口創、 真下哲郎、三原智、森俊則、八島純、山下了、吉村浩司 東大理 折戸周治 早大理工総研 岡田宏之、菊池順、澤田龍、鈴木聡、 寺沢和洋、道家忠義、山下雅樹、吉村剛史 高エ研 久野良孝、杉本康博、春山富義、真木昌弘、山本明 名大 増田公明

  3. e+ μ+ γ Introduction μ＋→e＋γ • Charged lepton flavor violating (LFV) process • Forbidden in the Standard Model • Sensitive to physics beyond the Standard Model SUSY-GUT, SUSY+νR , … • Present experimental bound 　 Br(μ＋→e＋γ) < 1.2 x 10－11 (MEGA experiment) mμ2+me2 Ee= ~ 52.8MeV 2mμ • e+ and γ • Back-to-back • Coincident mμ2－me2 Eγ= ~ 52.8MeV 2mμ

  4. SUSY-GUT L.J.Hall et al. Nucl. Phys. B267(1986)415 SU(5) SUSY-GUT predicts Br（μ＋→e＋γ） ＝ 10-15 - 10-13 (SO(10) SUSY-GUT: even larger value 10-13 - 10-11)

  5. Neutrino Oscillation and SUSY “MSW small angle mixing’’ and “Just-so’’ are disfavored by recent Super Kamiokande results Signature of μ→eγ could be discovered at the sensitivity of Br ~ 10-14

  6. μ→eγsearch experiment at PSI • Liquid Xe photon detector • Positron spectrometer with gradient magnetic field • Thin superconducting solenoid • DC muon beam at PSI 108μ/sec Expected sensitivity Br(μ→eγ) ~ 10-14

  7. Sensitivity and Backgrounds Single event sensitivity Nμ=1x108/sec, T =2.2x107sec, Ω/4π=0.09, εγ=0.7,εe=0.95 Br(μ＋→e＋γ) ~ 0.94 x 10-14 Major backgrounds • Accidental　Coincidence • Michel decay(μ＋→e＋νeνμ) + random γ • Radiative muon decays (inner bremsstrahlung) • μ＋→e＋νeνμ γ

  8. Backgrounds can be suppressed well below 10-14 Expected Detector Performance Accidental background rate Baccidental∝ ΔEeΔteγ (ΔEγ )2(Δqeγ )2

  9. Positron Spectrometer Superconducting solenoid spectrometer with gradient magnetic field • Constant bending radius independent of emission angle • Positrons are quickly swept out Uniform field Gradient field Uniform field Gradient field See also : 西口創他　 μ＋→e＋γ崩壊探索実験のためのe＋ スペクトロメータの研究開発　(25pYE-10)

  10. Liquid Xenon photon detector • Scintillation light is viewed by ~800 PMTs (Mini-Kamiokande type) effective coverage ~ 35% • Good energy resolution • Fast response • Spatially uniform response See also : 八島純他　 μ＋→e＋γ崩壊探索実験の 高性能液体Xe photon detector の R&D 　(25pYE-9)

  11. Liquid Xenon as Scintillator • High light yield (75% of NaI(Tl)) • Fast signals • Spatially uniform response

  12. Properties of Liquid Xenon Scintillator

  13. R&D of PMT Hamamatsu R6041Q Dynode structure

  14. R&D of PMT R6041Q can be stably operated at liquid Xe temperature (165K)

  15. First Prototype of Liquid Xenon Detector • 32 x PMTs (R6041Q) • Active Xe volume 116 x 116 x 174 mm3

  16. PMT Frame of First Prototype

  17. Energy Resolution Measurements • Possible to achieve • s < 1% for 52.8MeVγ

  18. Position Resolution Measurements • Positions are determined by • means weighed by PMT output • Possible to achieve s < 1mm • for 52.8MeV γ

  19. Timing Resolution Measurements Possible to achieve σ~ 50psec for 52.8MeV γ

  20. PMT Calibration with Gas Xe • PMT calibration with scintillation light (175nm) from gas Xe • Quantum efficiency • Gain • Position dependence on photo-cathode plane • Movable α- source with collimator spread of light spot ~ 2mm • Operating temperature 190K – 300K

  21. Position Dependence on Photo-cathode Plane 300K 190K

  22. Liquid XenonLevel Meter • Capacitance level meter • Level resolution < 3mm

  23. Large Prototype of Liquid Xenon Detector • Prototype of larger size • 1/4 - 1/3 size of final detector • 264 PMTs • Measurement of • Resolutions for high energy γ Energy, timing, position,… • Light attenuation length, light absorption length • Establishment of calibration technique and cryogenics, , purification system, … • Tests with large prototype will start at the beginning of 2001 …

  24. Tests with High Energy Photon Beam • TERAS electron storage ring of Electrotechnical Laboratory (ETL) • Inverse Compton gamma rays with an energy up to 40MeV TERAS ETL electron LINAC facility See also : 豊川弘之他　蓄積リングTERASにおける汎用LCSラインの建設　(23aYC-2)

  25. Support structure of PMTs on the front wall of the large prototype G10 PMT Lucite

  26. Schedule of μ→eγsearch experiment • 2000 • Construction of large prototype of liquid Xe detector • R&D of positron tracker and timing counter • Beam test of positron tracker at PSI (18/10/200~) • Design work of superconducting solenoid • 2001 • Test with large prototype at ETL • Construction of superconducting solenoid (winding, cryostat,…) • Beam line studies at PSI • Design work of final version of liquid Xe detector • 2002 • Fabrication and assembly of detector component • Tests of each detector component • 2003 • Engineering/physics run

  27. Summary • New experiment to search for μ＋→e＋γwith a sensitivity of 10-14 at PSI is in preparation • R&D works of Liquid Xe photondetector with good energy and timing resolutions are under way • Performance of the liquid Xe detector for high energy γ will be checked with large prototype early 2001 • Preparations of other detector components are on-going • Engineering/physics run will be started in 2003

  28. Mechanical Analysis of Superconducting Solenoid Stress distribution in the coil　(cross-sectional view) Max 180MPa Center of the solenoid →

  29. Stray Magnetic Field in Liquid Xe detector Region • Iron yoke • Active shields (compensation coil) • PMT with fine mesh dynode structure

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