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A sensitive search for decay: the MEG experiment

A sensitive search for decay: the MEG experiment. Marco Grassi INFN, Pisa on behalf of the MEG Collaboration. Les Rencontres de Physique de la Vallée d’Aoste, La Thuile, March 10-15 2003. Outline. Physics motivations SUSY predictions Connection with neutrino oscillations

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A sensitive search for decay: the MEG experiment

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  1. A sensitive search for decay: the MEG experiment Marco Grassi INFN, Pisa on behalf of the MEG Collaboration Les Rencontres de Physique de la Vallée d’Aoste, La Thuile, March 10-15 2003 M. Grassi – INFN Pisa La Thuile - March 15th , 2003

  2. Outline Physics motivations SUSY predictions Connection with neutrino oscillations e signature Signal and Background The experimental setup The beam The positron spectrometer The timing counter The e.m. calorimeter (LXe) Trigger and DAQ Conclusions Sensitivity Time profile M. Grassi – INFN Pisa La Thuile - March 15th , 2003

  3. Physics motivation Lepton Flavour Violation (LFV) processes, like meg , teg , meee , me conversion, are negligibly small in the extended Standard Model (SM)with massive Dirac neutrinos (BR  10-50) Super-Symmetric extensions of the SM (SUSY-GUTs) with right handed neutrinos and see-saw mechanismmay produce LFV processes at significant rates Ame gdecay is therefore a clean (no SM contaminated) indication of Super Symmetry But… Are these rates accessible experimentally? M. Grassi – INFN Pisa La Thuile - March 15th , 2003

  4. Experimental limit Our goal SUSY indications LFV induced by finite slepton mixing through radiative corrections • SUSY SU(5) predictions BR (meg)  10-14  10-13 • SUSY SO(10) predictions BRSO(10) 100 BRSU(5) R. Barbieri et al., Phys. Lett. B338(1994) 212 R. Barbieri et al.,Nucl. Phys. B445(1995) 215 small tan(b) excluded by LEP results M. Grassi – INFN Pisa La Thuile - March 15th , 2003

  5. Experimental limit Our goal n-oscillation connection 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 M. Grassi – INFN Pisa La Thuile - March 15th , 2003

  6. m+e+g Experiments Comparison with other LFV searches: Two orders of magnitude improvement is required: experimental challenge! M. Grassi – INFN Pisa La Thuile - March 15th , 2003

  7. The MEG Collaboration INFN & Pisa UniversityA. Baldini, C. Bemporad, F.Cei, M.Grassi, F. Morsani, D. Nicolo’, R. Pazzi, F. Sergiampietri, G. Signorelli INFN & Pavia UniversityA.de Bari, P. Cattaneo, G. Cecchet INFN & Genova UniversityS. Dussoni, F. Gatti, D. Pergolesi 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 M. Grassi – INFN Pisa La Thuile - March 15th , 2003

  8. 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 M. Grassi – INFN Pisa La Thuile - March 15th , 2003

  9. 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 M. Grassi – INFN Pisa La Thuile - March 15th , 2003

  10. 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 M. Grassi – INFN Pisa La Thuile - March 15th , 2003

  11. Primary proton beam The muon beam Exist Provide continuous>108 /s (with e+ contamination) Two separate configurations of thepE5beam line Muon momentum 29 MeV/c M. Grassi – INFN Pisa La Thuile - March 15th , 2003

  12. 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 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 OK Final measurements on Z-branch are planned inApr/May 2003Design of the transport solenoid is started M. Grassi – INFN Pisa La Thuile - March 15th , 2003

  13. 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 M. Grassi – INFN Pisa La Thuile - March 15th , 2003

  14. The solenoids • Bc = 1.26T current = 359A • Five coils with three different diameter • 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 Spectrometer ready to be shipped at PSI within this year OK M. Grassi – INFN Pisa La Thuile - March 15th , 2003

  15. 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) M. Grassi – INFN Pisa La Thuile - March 15th , 2003

  16. Drift chambers R&D (1) 90Sr source Tokyo Univ. OK (no magnetic field  full prototype test at PSI at the end of the year) M. Grassi – INFN Pisa La Thuile - March 15th , 2003

  17. Drift chambers R&D (2) • Full scale test in November • Improved vernier strips structure(uniform resolution) • Summary of Drift Chamber simulation FWHM M. Grassi – INFN Pisa La Thuile - March 15th , 2003

  18. 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) M. Grassi – INFN Pisa La Thuile - March 15th , 2003

  19. 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 OK M. Grassi – INFN Pisa La Thuile - March 15th , 2003

  20. H.V. Refrigerator Signals Cooling pipe Vacuum for thermal insulation Al Honeycomb Liq. Xe window PMT filler Plastic 1.5m Liquid Xe calorimeter • 800 l of Liquid Xe • ~800 PMT immersed in LXe • Only scintillation light • High luminosity • Unsegmented volume Experimental check M. Grassi – INFN Pisa La Thuile - March 15th , 2003

  21. 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  4.5% FWHM(E)/E (%) M. Grassi – INFN Pisa La Thuile - March 15th , 2003

  22. 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 M. Grassi – INFN Pisa La Thuile - March 15th , 2003

  23. -sources The LP LEDs M. Grassi – INFN Pisa La Thuile - March 15th , 2003

  24. 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 @ 90% C.L. OK M. Grassi – INFN Pisa La Thuile - March 15th , 2003

  25. 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 • 214Bi 208Tl ?? • 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 M. Grassi – INFN Pisa La Thuile - March 15th , 2003

  26. 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 improved QE 5 10% 52.8Mev OK M. Grassi – INFN Pisa La Thuile - March 15th , 2003

  27. 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 M. Grassi – INFN Pisa La Thuile - March 15th , 2003

  28. Readout electronics Waveform digitizing for all channels Custom domino sampling chip designed at PSI Cost per DSC ~ 1 US$ 2.5 GHz sampling speed @ 40 ps timing resolution Sampling depth 1024 bins Readout similar to trigger Prototypes delivered in autumn M. Grassi – INFN Pisa La Thuile - March 15th , 2003

  29. Detector parameters Signal Single Event Sensitivity  410-14 Cuts at 1,4FWHM  3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 M. Grassi – INFN Pisa La Thuile - March 15th , 2003

  30. 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 • The 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 November 2003 • Large Prototype for energy, position and timing resolutions of gs • Full scale Drift Chamber • -Transport and degrader-target • Final approval requested to INFN-CSN1 • Tentative time profile http://meg.psi.ch http://meg.pi.infn.it http://meg.icepp.s.u-tokyo.ac.jp More details at M. Grassi – INFN Pisa La Thuile - March 15th , 2003

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