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MEG Experiment at PSI R&D of Liquid Xenon Photon Detector

R&D work on a Liquid Xenon Detector for the m  e g Experiment at PSI on behalf of the MEG Collaboration University of Tokyo, Japan Presented by S. Mihara http://meg.psi.ch. MEG Experiment at PSI R&D of Liquid Xenon Photon Detector. m  e g Search as Frontier Physics. m e g in…

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MEG Experiment at PSI R&D of Liquid Xenon Photon Detector

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  1. R&D work on a Liquid XenonDetector for the meg Experiment at PSIon behalf of the MEG Collaboration University of Tokyo, Japan Presented by S. Miharahttp://meg.psi.ch MEG Experiment at PSI R&D of Liquid Xenon Photon Detector

  2. me g Search asFrontier Physics • meg in… • SM+Neutrino Oscillation • Suppressed as ∝(mn/mW)4 • SUSY • Large top Yukawa coupling Current limit by MEGA • Neutrino Oscillation + SUSY • Hisano and Nomura 1998 10-10 tanb nm ne 10-11 e m W 10-12 g Br(meg) 10-13 Solar Neutrino 10-14 g 10-15 ~ ~ m e MnR(GeV) SK+SNO etc.=Large Mixing Solution ~ c m e

  3. MEG Experiment Overview • Detect e+and g, “back to back” and “in time” • 100% duty factor continuous beam of ~ 108m/sec • better than pulsed beam to reduce pile-up events • Two characteristic components • Liquid Xe photon detector • Solenoidal magnetic spectrometer with a graded magnetic field (COBRA)

  4. menn+”g” n n g e ? Signal and Background Signal qeg= 180° m g e • Signal • Main background sources • Radiative m+ decay • If neutrinos carry small amount of energy, the positron and gamma can mimic the signal. • Accidental overlap • A positron from usual Michel decay with energy of half of mm • Gamma from • Radiative muon decay or • Annihilation in flight of positron NOT back to back, NOT in time Ee = 52.8 MeV Eg = 52.8 MeV menng g n n e

  5. Requirement onthe Photon Detector • Good resolutions • Energy • Position • Time • Large acceptance with good uniformity • Fast decay time to reduce pile-up events

  6. Property Unit Saturated temperature T(K) 164.78 Saturated pressure P(MPa) 0.100 Latent heat (for liquid) r(J/kg)X103 95.8 Latent heat (for solid) r'(J/kg)X103 1.2 Specific heat Cp(J/kgK)X103 0.3484 Density r(kg/m3)X103 2.947 Thermal conductivity k(W/mK) 0.108 Viscosity m(Pa-s)X10-4 5.08 Surface tension s(N/m)X10-3 18.46 Expansion coefficient b(1/K)X10-3 2.43 Temperature/Pressure at triple point Tt(K)/PT(MPa) 161.36/ 0.0815 Properties of Xenon • Fast response, Good Energy, and Position resolutions • Wph = 24 eV (c.f. Wph(NaI) = 17eV) • tfast=4.2nsec tslow=22nsec • Narrow temperature range between liquid and solid phases • Stable temperature control with a pulse-tube refrigerator

  7. Liquid XenonPhoton Detector Shallow event 800 liter LXe viewed by ~ 800PMTs Deep event

  8. Absorption of Scintillation Light Simulation For Large Prototype labs=7cm • Scintillation light emission from an excited molecule • Xe+Xe*Xe2*2Xe + hn • Water contamination absorbs scintillation light more strongly than oxygen. Depth parameter labs=500cm Depth parameter Depth

  9. R&D Strategy • Small Prototype done • Proof-of-Principle Experiment • 2.3liter active volume • Large Prototype in progress • Establish operation technique • 70 liter active volume • Final Detector starting • ~800 liter

  10. Small Prototype • 32 2-inch PMTs surround the active volume of 2.34 liter • g-ray sources of Cr,Cs,Mn, and Y • asource for PMT calibration • Operating conditions • Cooling & liquefaction using liquid nitrogen • Pressure controlled • PMT operation of 1.0x106 gain • Proof-of-Principle Experiment • PMT works in liquid xenon? • Light yield estimation is correct? • Simple setup to simulate and easy to understand. S.Mihara et al. IEEE TNS 49:588-591, 2002

  11. Small PrototypeEnergy resolution • Results are compared with MC prediction. • Simulation of g int. and energy deposition : EGS4 • Simulation of the propagation of scint. Light EGS cut off energy : 1keV Rayleigh Scattering Length: 29cm Wph = 24eV

  12. Small PrototypePosition and Timing resolutions • PMTs are divided into two groups by the y-z plane • gint. positions are calculated in each group and then compared with each other. • Position resolution is estimated as sz1-z2/√2 • The time resolution is estimated by taking the difference between two groups. • Resolution improves as ～1/√Npe

  13. Large Prototype • 70 liter active volume (120 liter LXe in use) • Development of purification system for xenon • Total system check in a realistic operating condition: • Monitoring/controlling systems • Sensors, liquid N2 flow control, refrigerator operation, etc. • Components such as • Feedthrough,support structure for the PMTs, HV/signal connectors etc. • PMT long term operation at low temperature • Performance test using • 10, 20, 40MeV Compton g beam • 60MeV Electron beam

  14. Gas return To purifier Circulation pump Purification System • Enomoto Micro Pump MX-808ST-S • 25 liter/m • Teflon, SUS • Xenon extracted from the chamber ispurified by passing through the getter. • Purified xenon is returned to the chamber and liquefied again. • Circulation speed 5-6cc/minute

  15. Purification Performance • 3 sets of Cosmic-ray trigger counters • 241Am alpha sources on the PMT holder • Stable detector operation for more than 1200 hours Cosmic-ray events a events

  16. Absorption Length • Fit the data with a function : A exp(-x/ labs) • labs >100cm (95% C.L) from comparison with MC. • CR data indicate that labs > 100cm has been achieved after purification.

  17. Response to Gamma Beam • Electron storage ring, TERAS, in AIST, Tsukuba Japan • Electron Energy, Current: 762MeV, 200mA • 266nm laser to induce inverse-Compston scattering. • 40 MeV (20MeV, and 10MeV) Compton g provided. • The Compton edge is used to evaluate the resolution. • Data taking • Feb. 2002 (w/o purification) • Apr. 2003 (w/ purification) 10MeV 20MeV 40MeV

  18. Energy Spectrum • s2 :depth parameter: 40MeV Compton gamma data w/o xenon purification 40MeV Compton gamma data w/ xenon purification Depth parameter Depth parameter Total Number of Photoelectrons Total Number of Photoelectrons

  19. Energy Resolution Simulation 52.8MeV g • Shallow events have dependence on the depth of the 1st int. point. • Discard these shallow events (~34%) for quick analysis. • Calibration not completed • Very Preliminary: sE < 2% Depth parameter Very Preliminary

  20. Position Reconstruction • 2-step reconstruction • 1st step: Pre-determination of the peak • 2nd step: Precise determination with an iteration process • Data 40MeV Compton g (a) (b) (c) (d)

  21. Timing Resolution • Estimated using Electron Beam (60MeV) data • Resolution improves in proportion to 1/sqrt(Npe). • For 52.8 MeV g, s~60 psec + depth resolution. • QE improvement and wave-form analysis will help to achieve better resolution. (Visit “The DRS chip” by S.Ritt) s=75.6+/-2.0ps 45 MeV Energy deposit by 60 MeV electron injection s Timing Resolution (psec) 52.8MeV g (nsec) 104 4x104 Number of Photoelectron

  22. Summary • New experiment to search for meg at Paul Scherrer Institut • Two characteristic components (and many others) • Liquid Xenon Photon Detector • Solenoidal magnetic spectrometer with a graded magnetic field (COBRA) • R&D of liquid xenon photon detector using the large prototype • Long term stable operation using a pulse tube refrigerator • Purification of liquid xenon • Very preliminary result from the last g beam test • sE<2% for 40MeV Compton g

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