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Liquid Xenon Detector for the MEG Experiment

Liquid Xenon Detector for the MEG Experiment. Toshiyuki Iwamoto 4/Oct/2006 10 th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD06) Siena. MEG Physics. Lepton flavor violating process already violated in neutrino sector Forbidden in the Standard Model

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Liquid Xenon Detector for the MEG Experiment

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  1. Liquid Xenon Detector for the MEG Experiment Toshiyuki Iwamoto 4/Oct/2006 10th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD06) Siena Siena 2006

  2. MEG Physics • Lepton flavor violating process • already violated in neutrino sector • Forbidden in the Standard Model • Sensitive to the new physics models, SUSY GUT, or SUSY seesaw etc. • The present experimental limit • ~ 1.2x10-11 by MEGA experiment Clear 2-body kinematics Ee = Eg = 52.8 MeV Back to back (qeg = 180°) Simultaneous (Te = Tg) Siena 2006

  3. Sensitivity Background Radiative m decay : m+ e+nm neg < 10-14 Accidental overlap: m decay m  en n + random g To reject these background, energy, timing and vertex resolution pile-up rejection from waveform analysis Single event sensitivity ~ 4x10-14 Background event ~ 4x10-14 90% C.L. sensitivity ~ 1x10-13 photon detector requirement DEg = 5% (FWHM) DTg = 150ps (FWHM) DXg = 9mm (FWHM) MEGA MEG Siena 2006

  4. MEG detector Approved in 1999 at PSI Physics run in 2007 Siena 2006

  5. MEG Detector 590 MeV proton Ring Cyclotron Drift chamber COBRA magnet w/ graded B field Most intense DC muon beam (108/s) H. Nishiguchi, 5th Oct “The MEG positron spectrometer” Timing counter Photon detector Siena 2006

  6. Photon Detector 800 liter liquid xenon, 846 2” PMTs in liquid High light yield, fast response and good uniformity (~40000ph/MeV, t=4.2, 22, 45ns) Low temperature (~160K), l = 178nm : development of PMT, refrigerator Xenon purity : remove H2O Performance test of Xe detector 2.3 liter prototype confirmed the principle of Xe 68.6 liter prototype 10, 20, and 40 MeV inverse Compton scattering g energy,timing and vertex resolution 55, 83MeV, 129MeV g from p-p->np0,ng reaction energy, and timing resolution Siena 2006

  7. Improvement PMT Q.E. : ~15% Photocathode : K-Cs-Sb Metal channel dynode, 12 stages Silica window (for UV light) Compact, and low heat load Tolerance up to 100G magnetic field Al strip to keep surface resistance at low temp. Zener diode for high rate background Purification Gas & Liquid phase purification tested Metal getter (zirconium) by gas ~0.5l/h Molecular sieves by liquid ~100l/h 1m 57mm 2.5m Siena 2006

  8. Prototype test, 10~40MeV g 68.6l liquid xenon prototype detector 228 PMTs 40MeV g Energy 1.6% in s s ~ 4mm Vertex distribution Siena 2006

  9. Energy (MeV) Opening angle (q) Prototype test, 55~129MeV g 83MeV H2 target Prototype LXe LYSO g g 175° 170° NaI 55MeV p- m phe Xenon detector p- (at rest) + p -> p0 + n, p0(28MeV/c) -> g + g (54.9MeV<Eg<82.9MeV) Almost monochromatic g is available p- + p -> n + g (129MeV) Energy, timing resolution neutron response Siena 2006 ENaI + ELYSO (MeV)

  10. Photon detector performance Energy distribution @ 55MeV 5% 1% Energy resolution vs. Energy • = 1.23 ±0.09 % FWHM=4.8 % Energy Resolution (s) [%] Timing distribution 110 psec Expected Performance Energy : 5% (FWHM) Timing : 150 psec (FWHM) Vertex : 9mm (FWHM) 110 - 64 (LYSO) - 61 (Beam) = 65psec Siena 2006

  11. Detector operation 250l gas xenon tank x 8 purifier Refrigerator 1000l liquid xenon storage tank Siena 2006

  12. Calibration method • Gain monitor : LED • Q.E. : 241Am a source • Energy • 55, 83, and 129 MeV g from p-pp0n, p02g • Ni thermal n capture 9MeV • Proton accelerator • Li(p,)Be 17.6MeV • B(p,)C 16.1MeV • Timing • Laser • radiative m decay • 55 MeV g from p-pp0n reaction (Pb+Scintillator) • Vertex • 55 MeV g from p-pp0n reaction (collimator) 3x3 NaI array LH2 target Siena 2006

  13. Detector Construction Siena 2006

  14. Detector Construction top outer side inner The performance of all PMTs checked in the liquid xenon before installation Siena 2006

  15. Schedule • Cryostat will come to PSI in the end of this year • PMT installation into holders almost done • Liquid xenon detector assembly will be done in the beginning of next year, and then liquefaction, purification and stable operation test will be continued. • physics run starts in 2007 • Positron spectrometer run and calibration run will be done in this year Siena 2006

  16. Summary • MEG experiment will search for m->eg with better sensitivity than previous experiment • The performance of liquid xenon detector has been tested by using prototype, and the real detector is being constructed • Physics run of MEG experiment will start in 2007. • Positron spectrometer data and calibration data will be taken in this year. Siena 2006

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