1. Status of the MEG Experiment W. Ootani ICEPP, University of Tokyo for the MEG collaboration

2. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002 Outline Physics motivations for the MEG experiment Physics motivations for the MEG experiment MEG detector MEG detector Status of the sub-detectors Status of the sub-detectors  Beam line  Photon detector  Positron spectrometer Magnet Magnet Drift chamber Drift chamber Timing counter Timing counter  Trigger, DAQ, and slow control Summary Summary

3. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002 MEG Collaboration A. Baldini 4, A. de Bari 5, L. M. Barkov 1, C. Bemporad 4, P.Cattaneo 5, G. Cecchet 5, F. Cei 4, T. Doke 8, J. Egger 6, M.Grassi 4, A. A. Grebenuk 1, T. Haruyama 4, P. -R. Kettle 6, B. Khazin 1, J. Kikuchi 8, Y. Kuno 3, A. Maki 2, Y. Makida 2, T. Mashimo 7, S. Mihara 7, T. Mitsuhashi 7, T. Mori 7, D. Nocolò 4, H. Nishiguchi 7, H. Okada 8, W. Ootani 7, K. Ozone 7, R. Pazzi 4, S. Ritt 6, H. Nishiguchi 7, H. Okada 8, W. Ootani 7, K. Ozone 7, R. Pazzi 4, S. Ritt 6, T. Saeki 7, R. Sawada 7, F. Sergiampietri 4, G. Signorelli 4, V. P. Smakhtin 1, S. Suzuki 8, K. Terasawa 8, A. Yamamoto 2, M. Yamashita 7, K. Yoshimura 2, T. Yoshimura 8 1 BINP, Novosibirsk, Russia 2 KEK, Tsukaba, Japan 3 Osaka University, Osaka, Japan 4 INFN, University and Scuola Normale Superiore, Pisa, Italy 5 INFN and University of Pavia, Pavia, Italy 6 PSI Villigen, Switzerland 7 University of Tokyo, Tokyo, Japan 8 Waseda University, Tokyo, Japan

4. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002   e  Event signature Event signature Back to back Back to back Time coincident Time coincident E e = E  = 52.8MeV E e = E  = 52.8MeV Lepton-family-number nonconserving process Lepton-family-number nonconserving process Extremely small branching ratio in the standard model with finite neutrino mass Extremely small branching ratio in the standard model with finite neutrino mass ex.) BR(   e  )~10 -52 for m ~0.05eV ex.) BR(   e  )~10 -52 for m ~0.05eV Sensitive to physics beyond the standard model Sensitive to physics beyond the standard model SUSY-GUT, SUSY+ν R, … SUSY-GUT, SUSY+ν R, … Present experimental bound Present experimental bound BR(μ ＋ →e ＋ γ) < 1.2 x 10 － 11 (MEGA experiment, 1999) BR(μ ＋ →e ＋ γ) < 1.2 x 10 － 11 (MEGA experiment, 1999) New experiment with a sensitivity of BR~10 -14 planned at PSI New experiment with a sensitivity of BR~10 -14 planned at PSI μ+μ+ e+e+e+e+ γ

5. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002 Physics Motivations SU(5) SUSY-GUT predicts BR （   e  ） ＝ 10 -15 - 10 -13 SU(5) SUSY-GUT predicts BR （   e  ） ＝ 10 -15 - 10 -13 (SO(10) SUSY-GUT: even larger value 10 -13 - 10 -11 ) (SO(10) SUSY-GUT: even larger value 10 -13 - 10 -11 ) Small tan  excluded by LEP SUSY search Small tan  excluded by LEP SUSY search J. Hisano et al., Phys. Lett. B391 (1997) 341 Our goal

6. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002 Physics Motivations, cont’d After the recent SNO measurements... SNO collaboration, Q.R.Ahamd et al., PRL89(2002)010302 SUSY+ν R Our goal Solar meas. strongly favor the LMA. Solar meas. strongly favor the LMA. Large tan   large  e  rate Large tan   large  e  rate J.Hisano and D.Nomura, PRD59(1999)116005

7. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002 MEG Detector Liquid xenon photon detector Liquid xenon photon detector Positron spectrometer with Positron spectrometer with gradient magnetic field (COBRA gradient magnetic field (COBRA spectrometer) spectrometer) World’s most intense DC muon World’s most intense DC muon beam at PSI beam at PSI Sensitivity down to BR~10 -14 Sensitivity down to BR~10 -14 Engineering/physics run will start Engineering/physics run will start in 2004 in 2004

8. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002 Sensitivity and Background Major backgrounds Major backgrounds N  =1x10 8 /sec, T =2.2x10 7 sec,  /4  =0.09,   =0.7,  e =0.95 BR(  ＋ →e ＋  ) ~ 0.94 x 10 -14 Single event sensitivity Single event sensitivity Accidental Coincidence Accidental Coincidence Michel decay(μ ＋ →e ＋ ν e ν μ ) Michel decay(μ ＋ →e ＋ ν e ν μ ) + random γ + random γ B accidental ~ 5 x 10 -15 B accidental ~ 5 x 10 -15 Radiative muon decays Radiative muon decays μ ＋ →e ＋ ν e ν μ γ μ ＋ →e ＋ ν e ν μ γ B prompt ~ 10 -17 B prompt ~ 10 -17 ΔEeΔEeΔEeΔEe 0.7% (FWHM) ΔEγΔEγΔEγΔEγ 1.4 – 2.0 % (FWHM) ΔeγΔeγΔeγΔeγ 12 – 14 mrad(FWHM) ΔteγΔteγΔteγΔteγ 0.15 nsec (FWHM) Proposed detector performance These values could be changed according to the actually achieved performance of the detector.

9. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002 Beam Line DC muon beam rate above 10 8  /s DC muon beam rate above 10 8  /s at  E5 beam line at  E5 beam line Two beam branches (“U” and “Z”) Two beam branches (“U” and “Z”) Comparative study of the branches Comparative study of the branches is in progress. is in progress. Positron contamination can be Positron contamination can be reduced by: reduced by: (1) Combination of an energy degrader (1) Combination of an energy degrader and a magnetic selection and a magnetic selection (2) Wien filter (2) Wien filter Condition“Z”-branch“U”-branch No degrader, transmitted to zone 3.6x10 8  + /s 6.0x10 8 e + /s 3.5x10 8  + /s 1.6x10 9 e + /s Degrader at final focus 2.0x10 8  + /s3.2x10 7  + /s m/e ratio at Muon Peak 916.5 Decision on the choice of the beam branch will be made after the beam tests tests with “U”-branch in Aug.2002 and with “Z”-branch in Nov.2002 primary proton beam

10. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002 Liquid Xenon Photon Detector Current design n Active volume of LXe: ~800 liter n Scintillation light is collected by ~800 PMTs immersed in LXe by ~800 PMTs immersed in LXe n Compact PMT with metal channel dynode structure and quartz window (Hamamatsu R6041Q) (Hamamatsu R6041Q)  High light yield (75% of NaI(Tl)) High light yield (75% of NaI(Tl)) Fast signals Fast signals  avoid accidental pileups  avoid accidental pileups Spatially uniform response Spatially uniform response  no need for segmentation  no need for segmentation

11. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002 Photon Detector Prototype A total of 120 liter liquid xenon (active volume of 69 liter) A total of 120 liter liquid xenon (active volume of 69 liter) Viewed by 240 PMTs Viewed by 240 PMTs Large enough to test with ~50MeV  Large enough to test with ~50MeV  LEDs and  sources ( 241 Am) implemented for calibration LEDs and  sources ( 241 Am) implemented for calibration

12. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002 Gamma Beam Tests Performance test of large prototype using high-energy gamma rays Performance test of large prototype using high-energy gamma rays Laser Compton backscattering facility at TERAS electron storage ring Laser Compton backscattering facility at TERAS electron storage ring of AIST, Tsukuba, Japan of AIST, Tsukuba, Japan Gamma-ray beam with energy up to 40MeV Gamma-ray beam with energy up to 40MeV Energy resolution evaluated by spread of Compton edge Energy resolution evaluated by spread of Compton edge Position reconstructed by PMT output distribution with proper collimator Position reconstructed by PMT output distribution with proper collimator Timing reconstructed by averaging arrival time Timing reconstructed by averaging arrival time Beam test in Feb. 2002 Beam test in Feb. 2002 Energy spectrum of gamma beam with 1mm  collimator (simulation)

13. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002 Beam test in Feb. 2002 Observed amount of light from 40MeV  is smaller than expected. (~10%) Observed amount of light from 40MeV  is smaller than expected. (~10%) Strong correlation between the conversion depth and N pe Strong correlation between the conversion depth and N pe Worse position resolution than expected Worse position resolution than expected  can be explained by strong light absorption in LXe Position  2 : conversion depth parameter 50<  2 <55 Energy

14. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002 MC Predictions with Absorption Feb02 beam test MC:monochromatic 40MeV  Energy resolution Position resolution MC predictions indicate abs < 10cm in gamma beam test in Feb. 2002 MC predictions indicate abs < 10cm in gamma beam test in Feb. 2002 We need abs > 100cm at least for an energy resolution of a few % order We need abs > 100cm at least for an energy resolution of a few % order

15. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002 Light Absorption in LXe H 2 O, C 2 H 4, NH 3, O 2 can strongly absorb 175nm scintillation light from LXe  Contaminations in LXe? light from LXe  Contaminations in LXe? Mass spectrum for the remaining gas in the detector vessel He H2OH2O N2N2 O2O2 CO 2 Xe

16. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002 Purification New circulatory purification system is installed after the beam test New circulatory purification system is installed after the beam test in Feb.2002. in Feb.2002. Xenon vapor is purified in Zr-V-Fe getter and Oxisorb filter and Xenon vapor is purified in Zr-V-Fe getter and Oxisorb filter and recondensed by the refrigerator and LN 2 during the operation of recondensed by the refrigerator and LN 2 during the operation of the detector the detector Circulation speed 10-12cc liq./minute Circulation speed 10-12cc liq./minute

17. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002 Improvement of Light Yield Alpha event Cosmic ray event

18. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002 Absorption Length Estimation Absorption length is estimated by seeing the absorption of the light from the alpha source event and cosmic ray event. the alpha source event and cosmic ray event. Cosmic ray trigger setup 4 x alpha source inside

19. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002 Absorption Length Estimation, cont’d Both measurements(CR and  ) indicate abs ~100cm after the purification Cosmic ray Alpha

20. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002 Positron Spectrometer Thin superconducting magnet designed to form gradient magnetic field Thin superconducting magnet designed to form gradient magnetic field Drift chamber for positron tracking Drift chamber for positron tracking Scintillation counters for timing measurement Scintillation counters for timing measurement COBRA spectrometer

21. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002 Concept of COBRA Spectrometer Gradient field Uniform field COBRA : COnstant Bending RAdius Constant bending radius independent of emission angles Constant bending radius independent of emission angles Low energy positrons quickly swept out Low energy positrons quickly swept out

22. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002 Magnet Five coils with three different diameter to form gradient field Five coils with three different diameter to form gradient field B c = 1.26T, B z=1.25m =0.49T@ operating current = 359A B c = 1.26T, B z=1.25m =0.49T@ operating current = 359A Compensation coils to suppress the residual field around the LXe detector Compensation coils to suppress the residual field around the LXe detector down to ~50Gauss down to ~50Gauss High-strength aluminum stabilized superconductor High-strength aluminum stabilized superconductor  thin superconducting coil: 0.2X 0  thin superconducting coil: 0.2X 0

23. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002 Construction of the Magnet Central coil Magnet design was finalized after detailed mechanical Magnet design was finalized after detailed mechanical calculations and related experimental tests. calculations and related experimental tests. Winding of the cable is in progress @ Toshiba. Winding of the cable is in progress @ Toshiba. Excitation test for the central part of the magnet Excitation test for the central part of the magnet will be performed in October 2002. will be performed in October 2002. Central coilGradient coil Compensation coil Winding of the central coil

24. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002 Positron Tracker 17 chamber sectors aligned radially 17 chamber sectors aligned radially with 10°intervals with 10°intervals Two staggered arrays of drift cells Two staggered arrays of drift cells Chamber gas: He-C 2 H 6 mixture Chamber gas: He-C 2 H 6 mixture Vernier pattern on the cathode foil Vernier pattern on the cathode foil to determine z-position to determine z-position

25. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002 First Prototype of the Chamber Resolution(  ) Drift time measurement 100-150  m Vernier cathod measurement 425  m Charge division measurement 2cm Drift velocity and drift time 4-12ns Sr-90

26. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002 Chambers System R&D in PSI Two prototypes are under construction at PSI. Two prototypes are under construction at PSI. “Double cathode” test chamber “Double cathode” test chamber Two separated double-strip cathodes for Two separated double-strip cathodes for each chamber layer each chamber layer  homogeneous position sensitivity  homogeneous position sensitivity Test in 1 Tesla magnetic field Test in 1 Tesla magnetic field “Charge division” test chamber “Charge division” test chamber Charge division test Charge division test 1m-long W(330W/m) or Steel(1200W/m) 1m-long W(330W/m) or Steel(1200W/m) Supporting system is also under development. Supporting system is also under development.

27. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002 Timing Counter Two layers of scintillator hodoscopes placed at right angles with each other Two layers of scintillator hodoscopes placed at right angles with each other Outer: timing measurement Outer: timing measurement Inner: additional trigger information Inner: additional trigger information Goal  time ~ 50psec Goal  time ~ 50psec

28. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002 Timing Counter Prototype CORTES: Timing counter test facility with cosmic rays at INFN-Pisa Scintillator bar (5cm x t 1cm x 100cm long) Telescope of 8 x MSGC Measured resolutions  time ~60psec independent of incident position  time improves as ~1/√Npe  use thicker counter ~ t 2cm

29. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002 Trigger Electronics Beam rate 10 8 s -1 Beam rate 10 8 s -1 Fast LXe energy sum >45MeV 2x10 3 s -1 Fast LXe energy sum >45MeV 2x10 3 s -1  interaction point  interaction point e + hit point in timing counter e + hit point in timing counter Time correlation  -e + 200 s -1 Time correlation  -e + 200 s -1 Angular correlation 20 s -1 Angular correlation 20 s -1 Design and simulation of type1 board completed Design and simulation of type1 board completed Prototype board delivered in Pisa by this fall Prototype board delivered in Pisa by this fall Trigger system structure

30. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002 Slow Control New field bus system under development for a reliable control of New field bus system under development for a reliable control of cryogenics of LXe detector, superconducting magnet, cryogenics of LXe detector, superconducting magnet, high voltage supply high voltage supply Low cost (typ. 20 US$ per node) Low cost (typ. 20 US$ per node) Several prototypes have been built and tested at PSI Several prototypes have been built and tested at PSI See http://midas.psi.ch/mscb See http://midas.psi.ch/mscb http://midas.psi.ch/mscb

31. Wataru Ootani, ICEPP, University of Tokyo NP02, Kyoto, Sep. 27-29 2002 Summary R&D work on the sub-detectors for the MEG experiment are going well. R&D work on the sub-detectors for the MEG experiment are going well. Performance of the LXe photon detector prototype is improving thanks to Performance of the LXe photon detector prototype is improving thanks to the improvement of the light yield. the improvement of the light yield. A beam test of the photon detector prototype with the purified xenon A beam test of the photon detector prototype with the purified xenon will be performed in Oct. 2002. will be performed in Oct. 2002. Beam line tuning with the COBRA magnet and assembly of Beam line tuning with the COBRA magnet and assembly of the sub-detectors will start in 2003. the sub-detectors will start in 2003. Engineering run will start in 2004. Engineering run will start in 2004. Updated status can be seen at three mirrored sites: http://meg.icepp.s.u-tokyo.ac.jp/ http://meg.icepp.s.u-tokyo.ac.jp/http://meg.icepp.s.u-tokyo.ac.jp/ http://meg.psi.ch/ http://meg.psi.ch/http://meg.psi.ch/ http://meg.pi.infn.it/ http://meg.pi.infn.it/http://meg.pi.infn.it/