Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, Search for the Lepton Flavor Violating Decay  e  in the MEG Experiment Shuei YAMADA ICEPP, University of Tokyo for the MEG collaboration

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, Contents Physics Motivations Event Signature The MEG Experiment Schedule Summary

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, Physics Motivation  e  : Lepton Flavor Violating process Forbidden in the SM Sensitive to new physics SUSY GUT SUSY Seesaw Sensitivity down to ~ Present limit <1.2x (MEGA) J.Hisano et al., Phys.Lett.B391 (1997) 341

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, Polarized beam to measure angular distribution 68.3% 90.0% 95.4%  Might be able to distinguish models of GUT A = (|A L | 2 -|A R | 2 )/(|A L | 2 +|A R | 2 )

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15,  e  vs.  B(  e  )/B(  ) = ~10 -4  e  comparable to (or better than)  ee  BR Expt’l bound (MEGA) Expt’l bound (Belle) J.Hisano et al., Phys.Rev. D59 (1999)

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, Clear 2-body decay Back to Back E e =E  =52.8MeV Backgrounds Accidental overlap of  e +  from Michel decay :  e e    from radiative decay, e + -annihilation in flight Radiative  + decay:  e e   Event Signature

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, The MEG Experiment  Approved at Paul Scherrer Institut, Switzerland in 1999  Start physics run from 2006  Initial aim at , eventually down to Paul Scherrer Institut

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, The MEG Collaboration ICEPP, University of Tokyo Y. Hisamatsu, T. Iwamoto, T. Mashimo, S. Mihara, T. Mori, H. Natori, H. Nishiguchi, W. Ootani, K. Ozone, R. Sawada, Y. Uchiyama, S. Yamada, S. Yamashita Budker Institute, Novosibirsk L.M. Barkov, A.A. Grebenuk, D.G. Grigoriev, B, Khazin, N.M. Ryskulov, Yu. Yuri PSI, Villigen J. Egger, P.-R. Kettle, M. Hildebrandt, S. Ritt INFN & Pisa University A. Baldini, C. Bemporad, F. Cei, M. Grassi, F. Morsani, D. Nicolo’, R. Pazzi, F. Raffaelli, F. Sergiampietri, G. Signorelli INFN & Pavia University A.de Bari, P. Cattaneo, G. Cecchet, G. Nardo’, M. Rossella INFN & Genova University S. Dussoni, F. Gatti, D. Pergolesi, R. Valle INFN Roma I D. Zanello INFN & Lecce University S. Spagnolo, C. Chiri, P. Creti, M. Panareo, G. Palama’ KEK, Tsukuba T. Haruyama, A. Maki, Y. Makida, A. Yamamoto, K. Kasami Waseda University T. Doke, J. Kikuchi, T. Kotajima, S. Suzuki, K. Terasawa, A. Yamaguchi

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, The MEG Detector LXe Scintillation Detector Drift Chamber Timing Counter Compensation Coil COBRA Magnet 262cm 252cm Surface   beam (DC) ～ 0.25x10 8 /sec

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, The MEG Detector Most intense DC muon beam (10 8 /sec) Gradient magnetic field e + spectrometer Liquid Xe scintillation  -ray detector

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, Techniques to Enable the Experiment Most intense DC muon beam (10 8 /sec) COBRA magnet w/ gradient B field LXe scintillation  -ray detector

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, MeV > 1.8mA > 150days/year PSI Proton Cyclotron

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15,  +  E5  + / e + separator The MEG detector 590MeV Primary Proton Quadruple magnets Beam Transport Solenoid Bending magnets Degrader  E5  + Beamline target  Intense focused DC muon beam 10 7~8 /sec, ~  2cm  Surface muon beam : 28MeV/c

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, COBRA Spectrometer  COnstant Bending RAdius Independent of emission angles e + momentum easily used at trigger level reconstruction flat acceptance  Michel e + swept out quickly Reduce # of hits on the chamber Solenoid with a gradient filed

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, COBRA is already PSI !! Succeeded full excitation (Apr. 2004) Gradient field 200A (full excitation : 360A) Good agreement w/ calculation !

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, Drift Chamber Conventional DC Less materials to reduce e + annihilation

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15,  800 liter Liquid Xenon scintillator high light yield : 75% NaI(Tl) fast response : 45ns decay time good uniformity  850  2” PMTs Facing inwards like Super-Kamiokande Directly soaked in LXe  R&D with prototype Performance LXe purification ~165K  Construction starts this year LXe Scintillation  -ray Detector 

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, liter Prototype 70L fiducial volume 228  2” PMTs To verify performance & operation  beam

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, Task of the 100L Prototype Detector operation Refrigerator, monitoring system, electronics, LXe purification… Detector performance resolution 228  2” PMTs Hamamatsu R6041Q Soaked directly into LXe 165K Long term stability

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, LXe Purification Scintillation light absorbed by H 2 O & O 2 Achieved absorption length > 100cm (<100ppb level) Before purification After purification

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, Laser Compton  -ray Beam Test

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, Laser Compton  -ray Beam Test Inverse Compton  Energy : 10, 20, 40 MeV Incident position : detector center Estimate energy resolution using Compton edge 1.6% in  40MeV Compton edge  Energy 40MeV  Vertex distribution 3.8mm in 

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, CEX  0 Beam PSI   - beam  Liquid H 2 stopping target  Back-to-back 2   8x8 NaI array opposite detector opening angle energy  Sep-Dec 2003

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, CEX  0 Beam PSI 170°175° 54.9MeV82.9MeV Opening angle(deg) Energy (MeV) Energy (MeV) Monochromatic  55 & 83MeV  - (at rest) + p   0 + n  0 (28MeV)   +  (back-to-back, 54.9MeV<E  <82.9MeV) 129MeV  - + p  n +  Neutron response

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, Event Display

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15,  0 Event Sample Energy of NaI (MeV) Number of p.e. in Xenon -pn-pn -pn0, 02-pn0, 02

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, Energy 55MeV  Edge resolution is important to discriminate BKG Excellent energy resolution 4.5% FWHM

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, Energy Resolution Resolution (right  )[%] preliminary TERAS data PSI data

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15,  2" PMT (Hamamatsu R6041Q) t2.5mm Quartz window  Sensitive to VUV (178nm) Photocathode : Rb-Cs-Sb w/ Mn layer  low 165K Q.E. : 6% in LXe (incl. Collection eff.) Gain : V Metal Channel Dynode  thin and compact 3-atm pressure proof TTS 750psec Works stably within 0.5% 165K 57 mm 32 mm

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, Further Improvement Expected Improved PMT : Hamamatsu R9288 Standard Bi-alkali : Sb-K-Cs No Mn layer Al strip pattern to fit with dynode pattern ~3-4x Q.E. improvement Uniform Q.E.  Old PMTs ware used in 100L prototype Al strip

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, Another CEX  0 Beam Test Test for improved PMTs : ~100 improved + ~100 old PMT Final electronics & trigger setup 2004 PSI

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, Expected BKG & Sensitivity Expected detector resolution  E  : 4.5% (FWHM)  E e : 0.8% (FWHM)  e  : 18mrad (FWHM)  t e  : 141ps (FWHM) Expected BKG initial phase Accidental BKG : down to ~ Radiative  + decay : down to < Single event sensitivity B(  e  ) ~ Eventually down to w/ improved PMTs, etc. Experimentally verified by prototype

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, Schedule 2004 Oct- Another CEX beam test for LXe PSI w/ new PMTs (~100 new & ~100 old PMTs) mid 2005 finish detector components construction detector integration engineering run physics run

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, Summary The MEG experiment will search for a Lepton Flavor Violating process  +  e +  with sensitivity down to Under construction at PSI, Switzerland COBRA magnet is ready 100L prototype LXe  detector Has been tested around 52.8MeV Excellent energy 55MeV Beam test w/ new PMTs (2004 Oct-) Physics run will start in 2006

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, End of Slides

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, Electronics & Trigger Domino Ring Sampling chip Waveform digitizer sampling up to 4.5GHz 10ch x 1024bins Readout speed up to 100MHz Expected trigger rate : 20Hz Photon energy >45MeV Photon-positron timing correlation < 20ns Photon-positron opening angle ~ 180deg.

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, Purification System Xenon extracted from the chamber is purified 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 Gas return To purifier Circulation pump

Shuei YAMADA, ICEPP, University of tau04 Nara, Sep. 15, Single Event Sensitivity B(  e  )=1/{N  T (  /4  )  e    sel }=4.5x  N  =0.25x10 8 /sec, T=2.6x10 7 sec,  /4  =0.09,  e =0.90,   =0.6 and  sel =0.7