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MEG 2009 現状と展望

東京大学素粒子物理国際研究センター 岩本敏幸　他MEGコラボレーション 日本物理学会 2009 年秋季大会 甲南大学岡本キャンパス. MEG 2009 現状と展望. Contents. Detector performance in 2008 P roblems in 2008 and solutions for 2009 run DCH XEC TC Upgrade plan Waveform digitizer (DRS2 to DRS4) TC fiber readout into trigger Prospects in 2009.

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MEG 2009 現状と展望

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  1. 東京大学素粒子物理国際研究センター 岩本敏幸　他MEGコラボレーション 日本物理学会 2009年秋季大会 甲南大学岡本キャンパス MEG 2009 現状と展望

  2. Toshiyuki Iwamoto (ICEPP) JPS 2009 Autumn meeting, Konan University Contents • Detector performance in 2008 • Problems in 2008 and solutions for 2009 run • DCH • XEC • TC • Upgrade plan • Waveform digitizer (DRS2 to DRS4) • TC fiber readout into trigger • Prospects in 2009

  3. MEG detector performance in 2008 90% signal box Br(m+ e+g) < 3.0x10-11 (90% CL) (expected 90%CL sensitivity was 1.3x10-11)

  4. Toshiyuki Iwamoto (ICEPP) JPS 2009 Autumn meeting, Konan University Problems in 2008 • Drift chamber (DCH) Operation • Discharge problem • Lower efficiency • Worse sp, sq, sf • Timing counter fiber operation • Noisy, couldn’t be used for trigger • worse efficiency for e+ - gdirection match • Liquid xenon calorimeter (XEC) light yield • Light yield: less (~70% of prototype) • Because the light yield can be monitored by 17.6MeV CW calibration, gaseous purification was continued during physics run

  5. Toshiyuki Iwamoto (ICEPP) JPS 2009 Autumn meeting, Konan University Solutionsfor discharge problem • Investigated weak points for all HV connections • HV soldering spot on PCB, and HV via on PCB are suspicious • DCH discharge reproduced at Lab testfinally after many trials ! • Solutions • New design of PCB • Individual layers with only HV and only GND ( 3 -> 4 layers ) • Potting of HV soldering spot with epoxy

  6. After modification • Two chambers with new anode HV pcb into “Aquarium” to see long term operation with He/Ethane inside and pure He outside and nominal HV • 16 DC modules are mounted in the support structure inside the helium cabin. Signal check by nominal HV Helium Cabin Aquarium Stable operation is confirmed for ~ 5 months

  7. Expected performance (DCH) • Efficiency • ~ 3 times better by MC including DCH, DCH-TC matching efficiency • Resolution • Ee: tail part reduced • 374keV(60%), 1.06MeV(33%), 2.00MeV(7%) ~ 1.3% (2008) • qe, fe: 18-10mrad • These MC study will be verified by this year’s Michel data taken with the physics data

  8. Toshiyuki Iwamoto (ICEPP) JPS 2009 Autumn meeting, Konan University XEC detector maintenance • Detector maintenance during winter shutdown • Fix some (possible) leak positions • Fix bad PMTs • Gaseous purification for 900L xenon • In July 2009, XEC detector filled with liquid again • XEC detector’s been stable since then • Light yield monitoring by CW, alpha, CR • Liquid purification (~9 times volume circulation)

  9. Gaseous & Liquid purification Gaseous purification 8 x 250L gas storage tank XEC detector 1000L liquid storage tank Liquid purification

  10. New purifier system • O2 gettercartridge • Developed for LAr use at CERN • H2O also removed by Oxidization-reduction of Cu • New pump • speed ~ 180l/h • 43 hours operation •  7740l circulation  9 times circulation

  11. Light yield in 2009 • 17.6MeV g of Li(p,g)Be, Light yield monitoring X1.4 2009/7 2008/12 • Higher light yield ~ 40% improved • Consistent with prototype • sEg might be improved by this light yield increase

  12. g waveform • Resolution, energy scale will be measured by p0 calibration • before physics run 2008/9 2008/12 2009/7 Longer g waveform after purification g decay time ~ 45ns (as expected, ~30ns in last year)

  13. Toshiyuki Iwamoto (ICEPP) JPS 2009 Autumn meeting, Konan University TC modification • Plastic scintillating fiber + APD ( z measurement ) • To provide precise z position for online trigger • New front-end boards design • S/N ~ 8 (noise~40mV) • Shorter shaping time for trigger (250ns -> 20ns) • Direction match 66% >90% z f

  14. Direction match • To get back-to-back e+g events • g direction • Inner face PMT index with maximum charge in XEC detector (q, f) • e+ direction • TC bar counter (f) • TC bar counter charge asymmetry or TC fiber (q, or z) • Direction matching at trigger level • LUT based on MC • z reconstruction resolution • ~7cm at online by using TC bar charge asymmetry • ~5mm by using TC fiber

  15. Toshiyuki Iwamoto (ICEPP) JPS 2009 Autumn meeting, Konan University Electronics modification • Waveform digitizer (DRS2DRS4) • 700MHz ~ 5GHz, 8(+1) channels with 1024 storage cells • Eliminate temperature drifts • Linearity improved ( 0~1V ) • Timing accuracy below 30ps • Currently being tested • Trigger • Dead time reduction • Dynamic range • Some front face PMTs saturated with input range(0-1V) -> (0-2V) • Dedicated a trigger • Improved separation between a’s and g’s • Direction matching efficiency improvement by using TC APD information

  16. Toshiyuki Iwamoto (ICEPP) JPS 2009 Autumn meeting, Konan University Prospects in 2009 • Resolution improvement • sEg • g calibration • g light yield • sEe • sqe, sfe • sTeg • stable DC operation • Background level is still low • Limited by statistics • Efficiency improvement • e+ (~0.4) • Trigger efficiency (>0.9) • DAQ livetime • Less calibration time • Running Time ~ 8.6 week • In total, ~ 5 times better Expected sensitivity(90%CL) in 2009 ~ 2.4x10-12 ( ~5 times better)

  17. Toshiyuki Iwamoto (ICEPP) JPS 2009 Autumn meeting, Konan University Schedule • Other experiment had used pE5 beam line until the beginning of Aug. • All detectors are ready at Mid. Sep. • Calibration run until beg. Oct. • Physics run from Oct. ~ 3 months Aug Sep Oct Nov Dec Lamb shift experiment Detector installation p0 calibration Physics DAQ

  18. Toshiyuki Iwamoto (ICEPP) JPS 2009 Autumn meeting, Konan University Summary • In 2008 physics run, Br(meg)<3x10-11 (90%CL) • Main problem was DCH discharge, and this problem should be solved in this years run • Efficiencies, resolutions of all detectors will be improved, and 5 times better statistics than 2008 will be available in 2009. • All detectors will be ready in mid. Sep., and physics run will be started at Oct. 2009 after a calibration run using p0 in late Sep. • MEG sensitivity in 2009 will still be limited by statistics, and the expected sensitivity is ~5 times better (2.4x10-12 90%CL). Two more years will be needed to reach a 10-13 sensitivity goal. 素粒子実験領域シンポジウム主題：Japan-Korea Joint Symposium: Lepton Flavor Violation Experimental Search for LFV Muon Decay U-Tokyo ICEPPMori Toshinori

  19. Solution: Clear before write write clear “Ghost pulse” problem R After sampling a pulse, some residual charge remains in the capacitors on the next turn and can mimic wrong pulses “Ghost pulse” 2% @ 2 GHz

  20. p0 calibration p- • p-p  p0n  ggn • Back-to-back photons • 55, 83 MeV • Opposite detector • NaI + APD array • LH2 target • p- beam condition wasn’t the same as m+ beam ( many e- background ) • This year, 1/4 p- beam rate will be used to estimate energy, timing, position resolution as close condition as the m+ XEC NaI+APD LH2 g g

  21. Xe scintillation photon • Excitation process (fast) • Xe + Xe*  Xe*2  2Xe + hn • Recombination process (slow) • Xe+ + Xe  Xe+2 • Xe+2 + e  Xe** + Xe • Xe**  Xe* + heat • Xe + Xe*  Xe*2  2Xe + hn

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