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 October 18, 2004 ROME 2004, Italy, NSS-MIC Conference, N 7 Scintillation Detectors I

Contents n n n Motivation & Event Signature MEG Experiment & Detector Photon Detector TERAS Beam test p 0 beam test in PSI　　 Summary October 18, 2004 ROME 2004, Italy, NSS-MIC Conference, N 7 Scintillation Detectors I

Motivation & Event Signature m->eg branching ratio Present limit: 1. 2 x 10 -11 Ø LFV process Ø Forbidden in the SM Ø Sensitive to SUSY-GUT, SUSY-seesaw etc. Ø Our goal : Br(m->eg)>10 -13~10 -14 Clear 2 -body kinematics 52. 8 Me. V 180° 52. 8 Me. V Michel decay (μ＋→e＋νeνμ) + random γ 　　　　　Background Rate ~ 10 -14 Radiative muon decay (μ＋→e＋νeνμγ) 　　　　　Background Rate < 10 -14 October 18, 2004 Only allowed after Kam. LAND ROME 2004, Italy, NSS-MIC Conference, N 7 Scintillation Detectors I

MEG Experiment & Detector Approved in 1999, at Paul Scherrer Institut, in Switzerland Physics run in 2006 Initial goal at 10 -13, finally to 10 -14 COBRA Xe Detector 252 cm Timing Counter m+ beam : World’s most intense 　DC Beam 108 m+ /s g detector : 800 liter liquid xenon scintillation detector with 830 PMTs e+ detector : m+ solenoidal magnetic spectrometer with a gradient magnetic field (COBRA) October 18, 2004 262 cm Drift　Chamber ROME 2004, Italy, NSS-MIC Conference, N 7 Scintillation Detectors I

The MEG Collaboration ICEPP, University of Tokyo Y. Hisamatsu, T. Iwamoto, T. Mashimo, S. Mihara, T. Mori, H. Nishiguchi, W. Ootani, K. Ozone, T. Saeki, R. Sawada, S. Yamashita KEK, Tsukuba T. Haruyama, A. Maki, Y. Makida, A. Yamamoto, K. Yoshimura, K. Kasami Osaka University Y. Kuno Waseda University T. Doke, J. Kikuchi, S. Suzuki, K. Terasawa, A. Yamaguchi, T. Yoshimura INFN & Genova University S. Dussoni, F. Gatti, D. Pergolesi, R. Valle INFN & Lecce University S. Spagnolo, C. Chiri, P. Creti, M. Panareo, G. Palama’ INFN & Pavia University A. de Bari, P. Cattaneo, G. Cecchet, G. Nardo’, M. Rossella INFN & Pisa University A. 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, Villigen J. Egger, P. Kettle, M. Hildebrandt, S. Ritt Budker Institute, Novosibirsk L. M. Barkov, A. A. Grebenuk, D. G. Grigoriev, B, Khazin, N. M. Ryskulov October 18, 2004 ROME 2004, Italy, NSS-MIC Conference, N 7 Scintillation Detectors I

Photon Detector Ø 800 liter liquid xenon scintillation detector 830 PMTs directly filled into the liquid (effective coverage ~ 35%) ØHigh light yield (75% of Na. I(Tl) ), fast response (decay time ~4 ns) and good uniformity The strategy of R&D u Small prototype ( 2. 3 liter size ) ~Me. V region study with sources u Large prototype ( 68. 6 liter size ) 1. TERAS beam test energy resolution of 10~40 Me. V g timing and vertex resolution 2. p 0 beam test in PSI energy resolution of 53~129 Me. V g October 18, 2004 ROME 2004, Italy, NSS-MIC Conference, N 7 Scintillation Detectors I Liq. Xe g

Large Prototype Detector Large Prototype Smaller acceptance Xe detector Active volume : 68. 6 liter 228 2” PMTs (Hamamatsu R 6041 Q) To check performances and LN 2 free operation by cryocooler October 18, 2004 ROME 2004, Italy, NSS-MIC Conference, N 7 Scintillation Detectors I

1. TERAS Beam Test 40 Me. V g Energy Inverse Compton g Energy : 10, 20, 40 Me. V Incident Position : Detector Center Estimate Energy Resolution using Compton Edge 40 Me. V g Vertex distribution 1. 6% in s 3. 8 mm in s October 18, 2004 ROME 2004, Italy, NSS-MIC Conference, N 7 Scintillation Detectors I

0 p 0(28 Me. V/c) -> g + g Opening angle selection of two g’s monochromatic g 80 Me. V 55 Me. V - Energy (Me. V) 0 Beam Test at PSI p Concept p (at rest) + p -> p + n, 175° 170° 155° Opening angle (deg) 54. 9 Me. V 82. 9 Me. V Liquid H 2 Target October 18, 2004 ROME 2004, Italy, NSS-MIC Conference, N 7 Scintillation Detectors I Energy (Me. V) 180°

p 0 Beam Test at PSIXe l p- (at rest) + p -> p 0 + n, LP p 0(28 Me. V/c) -> g + g monochromatic g calibration of around 52. 8 Me. V l p- + p -> n(8. 9 Me. V) + g (129 Me. V) linearity check & neutron response 115 cm n 115 cm g 8 x 8 Na. I LP Xe total charge p-p->np 0, p 0 ->2 g pp-p->ng To get Energy Resolution 　　Select p 0 events 　　Select Na. I energy 　　Select incident position in Xe detector 　　Remove too shallow and too deep events Na. I Energy (Me. V) October 18, 2004 ROME 2004, Italy, NSS-MIC Conference, N 7 Scintillation Detectors I

Energy Resolution Energy resolution in right s(%) 5. 0 4. 0 preliminary 3. 0 TERAS data PSI data 2. 0 4. 5% FWHM 1. 0 Energy spectrum @ 54. 9 Me. V g FWHM = (4. 5± 0. 3)% s (right)=(1. 6± 0. 1)% This result satisfied our requirement October 18, 2004 Right s is a good function of energy photon statistics are still dominant, further improvement is expected by ~ 3 x. Q. E. PMT(R 9288) ROME 2004, Italy, NSS-MIC Conference, N 7 Scintillation Detectors I

Neutron Response in Large Prototype LP Xe total charge E(Na. I)>100 Me. V, Qsum<20000 p-p->np 0, p 0 ->2 g p-p->ng Xe detector response for 8. 9 Me. V neutron ~30 ns LP Xe TDC timing (ns) Neutron TOF ~ 30 ns (115 cm/0. 14 c) Neutron Kenergy=8. 9 Me. V No bias data for Xe Require the beam correlation October 18, 2004 It might be the first time to detect the fast neutron like 8. 9 Me. V in such a large scale Xe detector. 45% detection efficiency @0 Me. V th. 30% @1 Me. V th. ROME 2004, Italy, NSS-MIC Conference, N 7 Scintillation Detectors I

Summary n n n 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 10 Me. V to 129 Me. V, and the excellent energy resolution at around 52. 8 Me. V was shown in the PSI beam test. Physics run will start in 2006. October 18, 2004 ROME 2004, Italy, NSS-MIC Conference, N 7 Scintillation Detectors I