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Liquid Xenon Scintillation Detector for the MEG Experiment

Liquid Xenon Scintillation Detector for the MEG Experiment. Toshiyuki Iwamoto ICEPP, University of Tokyo, Japan for the MEG Collaboration. Contents. Motivation & Event Signature MEG Experiment & Detector Photon Detector TERAS Beam test p 0 beam test in PSI Summary. Clear 2-body

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Liquid Xenon Scintillation Detector for the MEG Experiment

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  1. Liquid Xenon Scintillation Detector for the MEG Experiment Toshiyuki Iwamoto ICEPP, University of Tokyo, Japan for the MEG Collaboration

  2. Contents • Motivation & Event Signature • MEG Experiment & Detector • Photon Detector • TERAS Beam test • p0 beam test in PSI • Summary ROME 2004, Italy, NSS-MIC Conference, N7 Scintillation Detectors I

  3. Clear 2-body kinematics 52.8 MeV 180° 52.8 MeV Motivation & Event Signature m->eg branching ratio Present limit: 1.2x10-11 • LFV process • Forbidden in the SM • Sensitive to SUSY-GUT, SUSY-seesaw etc. • Our goal : Br(m->eg)>10-13~10-14 Michel decay (μ＋→e＋νeνμ) + random γ Background Rate ~ 10-14 Radiative muon decay (μ＋→e＋νeνμγ) Background Rate < 10-14 Only allowed after KamLAND ROME 2004, Italy, NSS-MIC Conference, N7 Scintillation Detectors I

  4. MEG Experiment & Detector Xe Detector Approved in 1999, at Paul Scherrer Institut, in Switzerland COBRA 252cm Timing Counter Physics run in 2006 Initial goal at 10-13, finally to 10-14 m+ beam : World’s most intense DC Beam 108m+/s g detector : 800liter liquid xenon scintillation detector with 830 PMTs e+ detector: solenoidal magnetic spectrometer with a gradient magnetic field (COBRA) m+ 262cm DriftChamber ROME 2004, Italy, NSS-MIC Conference, N7 Scintillation Detectors I

  5. TheMEG 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, K. Kasami 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 ROME 2004, Italy, NSS-MIC Conference, N7 Scintillation Detectors I

  6. Photon Detector • 800 liter liquid xenon scintillation detector 830 PMTs directly filled into the liquid (effective coverage ~ 35%) • High light yield (75% of NaI(Tl) ), fast response (decay time ~4ns) and good uniformity • The strategy of R&D • Small prototype ( 2.3 liter size ) • ~MeV region study with sources • Large prototype ( 68.6 liter size ) 1.TERAS beam test energy resolution of 10~40MeV g timing and vertex resolution 2.p0 beam test in PSI energy resolution of 53~129MeV g Liq. Xe g ROME 2004, Italy, NSS-MIC Conference, N7 Scintillation Detectors I

  7. Large Prototype Detector Large Prototype Smaller acceptance Xe detector Active volume : 68.6 liter 228 2” PMTs (Hamamatsu R6041Q) To check performances and LN2 free operation by cryocooler ROME 2004, Italy, NSS-MIC Conference, N7 Scintillation Detectors I

  8. 1. TERAS Beam Test Inverse Compton g Energy : 10, 20, 40 MeV Incident Position : Detector Center Estimate Energy Resolution using Compton Edge 40MeV g Energy 40MeV g Vertex distribution 1.6% in s 3.8mm in s ROME 2004, Italy, NSS-MIC Conference, N7 Scintillation Detectors I

  9. 175° p0 Beam Test at PSI 80MeV Concept p- (at rest) + p -> p0 + n, p0(28MeV/c) -> g + g Energy (MeV) Opening angle selection of two g’s  monochromatic g 55MeV 170° 155° 180° Opening angle (deg) 54.9MeV 82.9MeV Liquid H2 Target Energy (MeV) ROME 2004, Italy, NSS-MIC Conference, N7 Scintillation Detectors I

  10. 115cm 115cm LP Xe 8x8NaI g n p- p0 Beam Test at PSI • p- (at rest) + p -> p0 + n, • p0(28MeV/c) -> g + g • monochromatic g calibration • of around 52.8MeV • p- + p -> n(8.9MeV) + g (129MeV) • linearity check & neutron response p-p->np0, p0->2g LP Xe total charge To get Energy Resolution Select p0 events Select NaI energy Select incident position in Xe detector Remove too shallow and too deep events p-p->ng NaI Energy (MeV) ROME 2004, Italy, NSS-MIC Conference, N7 Scintillation Detectors I

  11. Energy Resolution Energy resolution in right s(%) 5.0 4.0 preliminary 3.0 2.0 TERAS data PSI data 4.5% FWHM 1.0 Energy spectrum @ 54.9 MeV g FWHM = (4.5±0.3)% s (right)=(1.6±0.1)% This result satisfied our requirement Right s is a good function of energy photon statistics are still dominant, further improvement is expected by ~ 3xQ.E. PMT(R9288) ROME 2004, Italy, NSS-MIC Conference, N7 Scintillation Detectors I

  12. Neutron Response in Large Prototype E(NaI)>100MeV E(NaI)>100MeV, Qsum<20000 p-p->np0, p0->2g Xe detector response for 8.9MeV neutron LP Xe total charge p-p->ng ~30ns LP Xe TDC timing (ns) It might be the first time to detect the fast neutron like 8.9MeV in such a large scale Xe detector. 45% detection efficiency @0MeV th. 30% @1MeV th. Neutron TOF ~ 30ns (115cm/0.14c) Neutron Kenergy=8.9 MeV No bias data for Xe Require the beam correlation ROME 2004, Italy, NSS-MIC Conference, N7 Scintillation Detectors I

  13. Summary • MEG experiment will search for m->eg decay, to explore SUSY-GUT, and currently being prepared at Paul Scherrer Institut in Switzerland. • Large prototype of the xenon detector has been tested from 10MeV to 129MeV, and the excellent energy resolution at around 52.8MeV was shown in the PSI beam test. • Physics run will start in 2006. ROME 2004, Italy, NSS-MIC Conference, N7 Scintillation Detectors I

  14. End of Transparency ROME 2004, Italy, NSS-MIC Conference, N7 Scintillation Detectors I

  15. How much water contamination? Simulated data Measured/MC Before purification: ~10 ppm After purification: ~10 ppb ROME 2004, Italy, NSS-MIC Conference, N7 Scintillation Detectors I

  16. Absorption length estimation simulated data Measured / MC(abs=inf.) MC(abs=var.) / MC(abs=inf.) measured a data/simulated a data Comparing the two results, the absorption length is estimated to be over 3m (97.8% C.L.). ROME 2004, Italy, NSS-MIC Conference, N7 Scintillation Detectors I

  17. PMT (HAMAMATSU R6041Q) • Features • 2.5-mmt quartz window • Q.E.: 6% in LXe (TYP) (includes collection eff.) • Collection eff.: 79% (TYP) • 3-atm pressure proof • Gain: 106 (900V supplied TYP) • Metal Channel Dynodethin and compact • TTS: 750 psec (TYP) • Works stably within a fluctuation of 0.5 % at 165K 32 mm 57 mm ROME 2004, Italy, NSS-MIC Conference, N7 Scintillation Detectors I

  18. Motivation • Under high rate background, PMT output (old Type PMT, R6041Q) reduced by 10-20%. • This output deterioration has a time constant (order of 10min.): Related to the characteristics of photocathode whose surface resistance increases at low temperature. • Rb-Sc-Sb + Mn layer used in R6041Q • Not easy to obtain “high” gain. Need more alkali for higher gain. • Larger fraction of alkali changes the characteristic of PC at low temp. So, New Type PMTs, R9288 (TB series) were tested under high rate background environment. • K-Sc-Sb + Al strip used in R9288 • Al strip, instead of Mn layer, to fit with the dynode pattern Confirmed stable output. ( Reported in last BVR) But slight reduction of output in very high rate BG Add more Al Strip Al Strip Pattern • Low surface resistance R9288 ZA series ROME 2004, Italy, NSS-MIC Conference, N7 Scintillation Detectors I Yasuko HISAMATSU MEG VRVS Meeting @PSI June 2004

  19. Works on Design of PMT Final! • Two Issues to be solved: • Output deterioration caused by high rate background. • (Effects of ambient temperature on Photocathode ) • Ans. Reduce Surface Resistance by adding Aluminum Strip Pattern • 2. Shortage of Bleeder Circuit Current • Ans. Improve Design of the Circuit by adding Zener Diode Delivered from HPK in April Rate Dependence Test @ Liq.Xe HPK has started to work on new bleeder circuit design Yasuko HISAMATSU MEG VRVS Meeting @PSI June 2004 ROME 2004, Italy, NSS-MIC Conference, N7 Scintillation Detectors I

  20. Large Power Pulse Tube Cryocooler Technology transfered to Iwatani Co., Ltd Designed: 150 W @165K

  21. Gas return To purifier Circulation pump Purification System • 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 • Enomoto Micro Pump MX-808ST-S • 25 liter/m • Teflon, SUS ROME 2004, Italy, NSS-MIC Conference, N7 Scintillation Detectors I

  22. Beam Line Beam Transport Solenoid m+/e+ separator m+ beam line target MEG Detector 590MeV proton Bending magnet Degrader Quadruple magnets Surface muon beam : 28MeV/c Beam line design established World’s most intensive m+ beam: 107~8/s ROME 2004, Italy, NSS-MIC Conference, N7 Scintillation Detectors I

  23. COBRA Spectrometer COBRA magnet was already installed into the pE5 area in PSI. Constant bending radius independent of the emission angle e+ momentum easily used at trigger level Michel positrons are quickly swept out reduce the hit rate for stable operation ROME 2004, Italy, NSS-MIC Conference, N7 Scintillation Detectors I

  24. Signal & Background • Single event sensitivity Nm~2.5x107/s, T=2.6x107s, W/4p =0.09, eg=0.6, ee=0.9 Sensitivity (m ->eg) ~ 4.5x10-14 (1st phase, capable to Nm~1x108/s) • Background Accidental : Michel decay (μ＋→e＋νeνμ) + random γ Background Rate ~ 10-14 Radiative muon decays : μ＋→e＋νeνμγ BackgroundRate < 10-14 • Good energy, time and position resolutions are required for g, e+ detector. Expected detector resolution DEg : 4.5% (FWHM) DEe : 0.8% (FWHM) Dqeg : <19mrad (FWHM) Dt eg : <230ps (FWHM) ROME 2004, Italy, NSS-MIC Conference, N7 Scintillation Detectors I

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