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Status of the MEG experiment

This talk provides an overview of the MEG experiment, its physics motivations, detectors, and research and development efforts. The goal is to study lepton flavour violation induced by finite slepton mixing through radiative corrections, with a focus on the SUSY SO(10) and SUSY SU(5) predictions. The experiment aims to improve the experimental limits and requires two orders of magnitude improvement in sensitivity. Collaborators include various institutes and universities worldwide.

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Status of the MEG experiment

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  1. Status of the MEG experiment A. M. Baldini INFN Pisa http://meg.pi.infn.it

  2. Physics motivations General description of the experiment Detectors R&D Sensitivity of the experiment Time schedule Layout of this talk

  3. SUSY SU(5) predictions BR (meg)  10-14  10-13 SUSY SO(10) predictions BRSO(10) 100 BRSU(5) Experimental limit Our goal SUGRA indications LFV induced by finite slepton mixing through radiative corrections R. Barbieri et al., Phys. Lett. B338(1994) 212 R. Barbieri et al.,Nucl. Phys. B445(1995) 215 combinedLEP results favour tanb>10

  4. Combined LEP experiments: SUGRA MSSM

  5. SO10

  6. Experimental limit Our goal Connection with n-oscillations Additional contribution toslepton mixingfrom V21 (the matrix element responsible for solar neutrino deficit) J. Hisano, N. Nomura, Phys. Rev. D59 (1999) tan(b)=30 tan(b)=1 After SNO After Kamland in the Standard Model !!

  7. m+  e+g Experiments Comparison with other LFV searches: Two orders of magnitude improvement is required: toughexperimental challenge!

  8. The MEG collaboration INFN & Genova UniversityS. Dussoni, F. Gatti, D. Pergolesi, R. Valle INFN & Lecce UniversityG. Cataldi, S. Spagnolo, C. Chiri, P. Creti, F. Grancagnolo, M. Panareo 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 ICEPP, University of TokyoT. Mashimo, S. Mihara, T. Mitsuhashi, T. Mori, H. Nishiguchi, W. Ootani, K. Ozone, T. Saeki, R. Sawada, S. Yamashita KEK, TsukubaT. Haruyama, A. Maki, Y. Makida, A. Yamamoto, K. Yoshimura Osaka UniversityY. Kuno Waseda UniversityT. Doke, J. Kikuchi, H. Okada, S. Suzuki, K. Terasawa, M. Yamashita, T. Yoshimura PSI, VilligenJ. Egger, P. Kettle, H. Molte, S. Ritt Budker Institute, NovosibirskL.M. Barkov, A.A. Grebenuk, D.G. Grigoriev, B, Khazin, N.M. Ryskulov

  9. qeg = 180° e+ +g Ee= Eg=52.8MeV Experimental method Easy signal selection with +at rest • Detector outline • Stopped beam of >107 /sec in a 150 mm target • Liquid Xenon calorimeter for  detection (scintillation) • fast:4 / 22 / 45 ns • high LY: ~ 0.8 * NaI • short X0:2.77 cm • Solenoid spectrometer & drift chambers fore+ momentum • Scintillation counters for e+ timing

  10. e+ +g e+ +g n n n n e+ + Signal and background background signal eg accidental en n egn n ee  g g eZ  eZ g correlated egn n qeg = 180° Ee= Eg=52.8MeV Te = Tg g

  11. Required Performances The sensitivity is limited by the by the accidental background The  310-14 allows BR (meg) 10-13 but needs FWHM

  12. Detector Construction Switzerland Drift Chambers Beam Line DAQ Russia LXe Tests Purification Italy e+ counter Trigger LXe Calorimeter Japan LXe Calorimeter,Magneticspectrometer

  13. Primary proton beam The PSI pE5 beam

  14. Beam studies • Optimization of the beam elements: • Wien filterform/e separation • Solenoid to couplebeam and spectrometer • Degrader to reduce the momentum for a 150 mm target • Intermediate results: • U-version Z-version • Rm(total)1.3*108m+/s 1.3*108m+/s • Rm(after W.filter)7.3*107m+/s 9.5*107m+/s • Rm(after solenoid)sV6.5mm, sH5.5mmto be studied • m/e separation 11 s 7 s Measurements on Z-branch are going on in 2003Design of the transport solenoid is started

  15. Gradient field Uniform field Gradient field Uniform field COBRA spectrometer COnstantBendingRAdius(COBRA) spectrometer • Constant bending radius independent of emission angles • High pT positrons quickly swept out

  16. Gradient field

  17. The solenoids • Bc = 1.26T current = 359A • Five coils with three different diameters • Compensation coils to suppress the stray field around the LXe detector • High-strength aluminum stabilized superconductor • thin magnet • (1.46 cm Aluminum, 0.2 X0) • “Crash” Tests completed • Winding completed @TOSHIBA • Ready to be shipped at PSI during summer OK

  18. Positron Tracker • 17 chamber sectors aligned radially with 10°intervals • Two staggered arrays of drift cells • Chamber gas: He-C2H6 mixture • Vernier pattern to measure z-position made of 15 mm kapton foils (X,Y) ~200 mm (drift time) (Z) ~ 300 mm (charge division vernier strips)

  19. Drift chambers R&D (1) 90Sr source Tokyo Univ. OK (no magnetic field  full prototype test at PSI by the end of this year)

  20. Full scale test in November Improved vernier strips structure(more uniform resolution) Summary of Drift Chamber simulation Drift chambers R&D (2) FWHM

  21. (90% C.L.) as a function of longitudinal position resolution

  22. Positron Timing Counter BC404 • Two layers of scintillator read by PMTs placed at right angles with each other • Outer: timing measurement • Inner: additional trigger information • Goal time~ 40 psec (100 ps FWHM)

  23. Timing Counter R&D CORTES: Timing counter test facility with cosmic rays  • Scintillator bar (5cm x 1cm x 100cm long) • Telescope of 8 x MSGC • Measured resolutions • time~60psec independent of incident position • time improves as ~1/√Npe 2 cm thick

  24. 800 l of Liquid Xe ~800 PMT immersed in LXe Only scintillation light High luminosity Unsegmented volume H.V. Refrigerator Signals Cooling pipe Vacuum for thermal insulation Al Honeycomb Liq. Xe window PMT filler Plastic 1.5m Liquid Xe calorimeter Experimental check

  25. LXe performance Energy resolution strongly depends on optical properties of LXe • Complete MC simulations • At labs the resolution is dominated by photostatistics FWHM(E)/E 2.5%(including edge effects) • At labs Ldet limits from shower fluctuations + detector response  need of reconstruction algorithms • FWHM(E)/E  4% FWHM(E)/E (%)

  26. Xenon Calorimeter Prototype • The Large Prototype (LP) • 40 x 40 x 50 cm3 • 228 PMTs, 100 litres Lxe • (the largest in the World) • Purpose • Test cryogenic operation on along termand on alarge volume • Measure theLxe properties • Check the reconstruction methods • Measure the Energy, Position and Timing resolutions • with: • Cosmic rays • -sources • 60 MeV eˉfrom KSR storage ring • 40 MeV from TERAS Compton Backscattering • e+and 50 MeV from p° at PSI Planned in this year

  27. -sources The LP LEDs

  28. LP: LXe optical properties • First tests showed that the number of scintillation photons was MUCH LESS than expected • It improved with Xe cleaning: Oxysorb + gas getter + re-circulation (took time) • There were a strong absorption due to contaminants (mainly H2O) March 2002 Present... labs> 1m

  29. 40K (1.461 MeV) 208Tl (2.614 MeV) LP: Radioactive background • -trigger with 5106 gain • Geometrical cuts to exclude-sources • Energy scale: -source • 208Tl (2.59±0.06) MeV • 40K (1.42 ± 0.06) MeV • uniform on the front face • few 10 min (with non-dedicated trigger) • nice calibration for low energy’s Seen for the first time! Studies are going on: spatial distribution of background inside the detector

  30. Timing resolution test t = (z2 + sc2)1/2 = (802 + 602)1/2 ps = 100 ps (FWHM) z Time-jitter due to photon interaction point sc Scintillation time and photon statistics our goal Measurement ofsc2with 60 MeV electron beam • weighted average of the PMT TDCs time-walk corrected • scvsph.el. • extrapolation at 52.8Mev is ok • new PMT with QE • 5 25% 52.8 MeV peak 5% 10% 15%QE

  31. Cryostat (PMT test facility)

  32. 2 boards LXe inner face (312 PMT) . . . . . . 10 boards 20 boards 1 board LXe lateral faces (488 PMT: 4 to 1 fan-in) 1 board 2 x 48 Type1 Type1 Type1 Type1 Type1 Type1 Type1 Type1 Type1 12 boards 2 boards 3 16 16 3 16 3 . . . Timing counters (160 PMT) Type2 Type2 Type2 Type2 Type2 Type2 2 VME 6U 1 VME 9U 2 x 48 4 x 48 20 x 48 12 x 48 10 x 48 Trigger Electronics • Uses easily quantities: •  energy • Positron-  coincidence in time and direction • Built on a FADC-FPGA architecture • More complex algorithms implementable • Beam rate 108 s-1 • Fast LXe energy sum > 45MeV 2103 s-1 g interaction point (PMT of max charge) e+ hit point in timing counter • time correlation g – e+ 200 s-1 • angular correlation g – e+ 20 s-1 • Design and simulation of type1 board completed • Prototype board delivered • by late spring

  33. Readout electronics • Waveform digitizing for all channels • Custom domino sampling chip designed at PSI • 2.5 GHz sampling speed @ 40 ps timing resolution • Sampling depth 1024 bins • Readout similar to trigger Prototypes delivered in autumn

  34. Detector parameters Signal Single Event Sensitivity  410-14 Cuts at 1,4FWHM  210-14 Backgrounds  310-15 Sensitivity Summary Upper Limit at 90% CL BR (meg) 110-13 Discovery 4 events (P = 210-3) correspond BR = 210-13

  35. Revised document now LoI Proposal Planning R & D Assembly Data Taking 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 Summary and Time Scale • This experiment may provide a clean indication of New Physics • Measurements and detector simulation make us confident that we can reach the SES of 4 x 10-14 to meg (BR 10-13) • Final prototypes will be measured within this year • Large Prototype for energy, position and timing resolutions of gs • Full scale Drift Chamber • -Transport and degrader-target • Financed this year in Italy+Switzerland • Tentative time profile http://meg.psi.ch http://meg.pi.infn.it http://meg.icepp.s.u-tokyo.ac.jp More details at

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