1. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 20041 Search for the Lepton Flavor Violating Decay  e  in the MEG Experiment Shuei YAMADA ICEPP, University of Tokyo for the MEG collaboration

2. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 20042 Contents Physics Motivations Event Signature The MEG Experiment Schedule Summary

3. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 20043 Physics Motivation  e  : Lepton Flavor Violating process Forbidden in the SM Sensitive to new physics SUSY GUT SUSY Seesaw Sensitivity down to ~10 -14 Present limit <1.2x10 -11 (MEGA) J.Hisano et al., Phys.Lett.B391 (1997) 341

4. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 20044 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 )

5. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 20045  e  vs.  B(  e  )/B(  ) = 10 -3 ~10 -4  e  comparable to (or better than)  ee  10 -11 BR 10 -13 10 -15 10 -7 10 -9 10 -11 Expt’l bound (MEGA) Expt’l bound (Belle) J.Hisano et al., Phys.Rev. D59 (1999) 116005

6. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 20046 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

7. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 20047 The MEG Experiment  Approved at Paul Scherrer Institut, Switzerland in 1999  Start physics run from 2006  Initial aim at 10 -13, eventually down to 10 -14 Paul Scherrer Institut

8. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 20048 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

9. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 20049 The MEG Detector LXe Scintillation Detector Drift Chamber Timing Counter Compensation Coil COBRA Magnet 262cm 252cm Surface   beam (DC) ～ 0.25x10 8 /sec

10. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 200410 The MEG Detector Most intense DC muon beam (10 8 /sec) Gradient magnetic field e + spectrometer Liquid Xe scintillation  -ray detector

11. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 200411 3 Techniques to Enable the Experiment Most intense DC muon beam (10 8 /sec) COBRA magnet w/ gradient B field LXe scintillation  -ray detector

12. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 200412 590MeV > 1.8mA > 150days/year PSI Proton Cyclotron

13. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 200413  + Beam @  E5  + / e + separator The MEG detector 590MeV Primary Proton Quadruple magnets Beam Transport Solenoid Bending magnets Degrader  E5 area @PSI  + Beamline target  Intense focused DC muon beam 10 7~8 /sec, ~  2cm  Surface muon beam : 28MeV/c

14. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 200414 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

15. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 200415 COBRA is already working @ PSI !! Succeeded full excitation (Apr. 2004) Gradient field profile @ 200A (full excitation : 360A) Good agreement w/ calculation !

16. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 200416 Drift Chamber Conventional DC Less materials to reduce e + annihilation

17. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 200417  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 Operation @ ~165K  Construction starts this year LXe Scintillation  -ray Detector 

18. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 200418 100 liter Prototype 70L fiducial volume 228  2” PMTs To verify performance & operation  beam

19. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 200419 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 Operation @ 165K Long term stability

20. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 200420 LXe Purification Scintillation light absorbed by H 2 O & O 2 Achieved absorption length > 100cm (<100ppb level) Before purification After purification

21. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 200421 Laser Compton  -ray Beam Test

22. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 200422 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 

23. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 200423 CEX  0 Beam Test @ PSI   - beam  CEX @ Liquid H 2 stopping target  Back-to-back 2   8x8 NaI array opposite detector opening angle energy  Sep-Dec 2003

24. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 200424 CEX  0 Beam Test @ PSI 170°175° 54.9MeV82.9MeV Opening angle(deg) Energy (MeV) 155180 5580 55 80 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

25. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 200425 Event Display

26. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 200426  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

27. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 200427 Energy Spectrum @ 55MeV  Edge resolution is important to discriminate BKG Excellent energy resolution 4.5% FWHM

28. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 200428 Energy Resolution Resolution (right  )[%] 2.0 3.0 1.0 4.0 preliminary TERAS data PSI data

29. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 200429  2" PMT (Hamamatsu R6041Q) t2.5mm Quartz window  Sensitive to VUV (178nm) Photocathode : Rb-Cs-Sb w/ Mn layer  low resistance @ 165K Q.E. : 6% in LXe (incl. Collection eff.) Gain : 10 6 @ 900V Metal Channel Dynode  thin and compact 3-atm pressure proof TTS 750psec Works stably within 0.5% fluctuation @ 165K 57 mm 32 mm

30. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 200430 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

31. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 200431 Another CEX  0 Beam Test Test for improved PMTs : ~100 improved + ~100 old PMT Final electronics & trigger setup 2004 Oct- @ PSI

32. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 200432 Expected BKG & Sensitivity Expected detector resolution  E  : 4.5% (FWHM)  E e : 0.8% (FWHM)  e  : 18mrad (FWHM)  t e  : 141ps (FWHM) Expected BKG rate @ initial phase Accidental BKG : down to ~10 -14 Radiative  + decay : down to <10 -14 Single event sensitivity B(  e  ) ~10 -13 Eventually down to 10 -14 w/ improved PMTs, etc. Experimentally verified by prototype

33. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 200433 Schedule 2004 Oct- Another CEX beam test for LXe prototype @ PSI w/ new PMTs (~100 new & ~100 old PMTs) mid 2005 finish detector components construction 2005- detector integration engineering run 2006- physics run

34. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 200434 Summary The MEG experiment will search for a Lepton Flavor Violating process  +  e +  with sensitivity down to 10 -14 Under construction at PSI, Switzerland COBRA magnet is ready 100L prototype LXe  detector Has been tested around 52.8MeV Excellent energy resolution @ 55MeV Beam test w/ new PMTs (2004 Oct-) Physics run will start in 2006

35. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 200435 End of Slides

36. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 200436 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.

37. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 200437 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

38. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 200438 Single Event Sensitivity B(  e  )=1/{N  T (  /4  )  e    sel }=4.5x10 -14  N  =0.25x10 8 /sec, T=2.6x10 7 sec,  /4  =0.09,  e =0.90,   =0.6 and  sel =0.7