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A   e  search experiment at PSI Status and Prospects

A   e  search experiment at PSI Status and Prospects. Giovanni Signorelli Istituto Nazionale di Fisica Nucleare and Scuola Normale Superiore, Pisa (Italy) for the MEG collaboration. NUFACT02 London, July 1-6 2002. Outline. Physics motivation for a e experiment

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A   e  search experiment at PSI Status and Prospects

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  1. A  e  search experiment at PSI Status and Prospects Giovanni Signorelli Istituto Nazionale di Fisica Nucleare and Scuola Normale Superiore, Pisa (Italy) for the MEG collaboration NUFACT02 London, July 1-6 2002

  2. Outline • Physics motivation for a e experiment • Quick look at the e decay • The detector • Recent progress

  3. Physics Motivations • Lepton Flavour Violation is forbidden in the Standard Model • Extensions of the SM (SUSY-GUTs) generically predict LFV • SUSY SU(5) predictions: LFV induced by finite slepton mixing through radiative corrections. The mixing could be large due to the top-quark mass • in SU(5)  clear evidence for physics beyond the SM Exp. Bound J.Hisanoet al.,Phys. Lett. B391 (1997) 341 R. Barbieri et al.,Nucl. Phys. B445(1995) 215 SO(10) predicts even larger BR:

  4. SO(10) SUSY-GUT Models R. Ciafaloni, A. Romanino, A. Strumia, Nucl. Phys. B458 (1996) Present Limit (MEGA) BRe < 1.2 10-11

  5.  oscillations SU(5) with right-handed neutrinos Experimental Bound J. Hisano, N. Nomura, Phys. Rev. D59 (1999)

  6. The MEG Collaboration INFN & Pisa University A. Baldini C. Bemporad F. Cei M. Grassi D. Nicolò R. Pazzi G. Signorelli F. Sergiampietri INFN & Pavia University A. De Bari P. Cattaneo G. Cecchet ICEPP, University of Tokyo T. Mashimo S. Mihara T. Mitsuhashi T. Mori H. Nishiguchi W. Ootani K. Ozone T. Saeki R. Sawada S. Yamashita KEK, Tsukuba T. Haruyama A. Maki Y. Makida A. Yamamoto K. Yoshimura Osaka University Y. Kuno Waseda University T. Doke J. Kikuchi H. Okada S. Suzuki K. Terasawa M. Yamashita T. Yoshimura BINP, Novosibirsk L. M. Barkov A. A. Grebenuk B. I. Khazin V. P. Smakhtin PSI, Villigen J. Egger P-R. Kettle S. Ritt

  7. Experimental Search for  e   = back-to-back • Stopped -beam: 108 /sec • Liquid Xenon calorimeter for  detection (scintillation) • fast: 4 / 22 / 45 ns • high LY: ~ NaI • Short X0: 2.77 cm • Solenoid spectrometer & drift chambers • Timing Counter for e+ timing e  E = 52.8 MeV E = 52.8 MeV

  8. Present Design Switzerland Drift Chamber, Beam Line, DAQ Russia LXe Tests and Purification Italy e+ counter, Trigger, M.C. LXe Calorimeter Japan LXe Calorimeter,Superconducting Solenoid, M.C.

  9. Signal and Background “Signal” “Prompt” “Accidental”      e e e e e ee  e e ee 

  10. Sensitivity and Background Rate The sensitivity of the experiment is limited by accidental background ? e 

  11. Beam Transport System at PSI • Must provide continuous 108 /sec with few e+ contamination • Two separate configurations of thepE5beam line, “U”-branch and “Z”-branch (29 MeV/c ’s) Primary proton beam

  12. U/Z-Branch Comparison • Spot size:23 mm horizontally • 68 mm vertically (FWHM)  focusing of 108 +/s on a thin target on a small spot (50 mm x 50 mm) • 8 weeks beam time is planned in 2002 (4w in July/Aug and 4w in Nov) • Electrostatic separator in “U”-branch • Study of focusing on “Z”-branch

  13. COBRA spectrometer COnstant Bending RAdius (COBRA) spectrometer • Constant bending radius independent of emission angles Gradient field Uniform field • Low energy positrons quickly swept out Gradient field Uniform field

  14. COBRA Magnet • Bc = 1.26T, operating current = 359A • Five coils with three different diameter to realize gradient field • Compensation coils to suppress the residual field around the LXe detector • High-strength aluminum stabilized superconductor thin superconducting coil (1.46 cm Aluminum, 0.2 X0) • Cable delivered • “Crash” Tests completed • Winding in progress @ TOSHIBA

  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 determine z-position (X,Y) (Z) ~ charge division

  16. Drift Chamber 90Sr source Tokyo Univ. (no magnetic field here  test in PSI)

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

  18. Positron Timing Counter, cont’d CORTES: Timing counter test facility with cosmic rays at INFN-Pisa • 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

  19. Trigger Electronics Trigger system structure VME boards • Uses easily quantities: •  energy cut (Npe) • Positron-  coincidence in time and direction • Built on a 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 in Pisa by this fall

  20. Slow Control System HV, T, P,… • New field bus system under development for reliable control of • cryogenics of LXe detector, superconducting magnet, • high voltage supply • Low cost (typ. 20 US$ per node) • Several prototypes have been built and tested at PSI • Seehttp://midas.psi.ch/mscb

  21. 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

  22. Xenon Calorimeter Prototype • Tests on the LXe calorimeter are currently under way in KEK Japan using a “LARGE PROTOTYPE”: • 40 x 40 x 50 cm3 • 264 PMTs, 100 litres Lxe • Used for the measurement of: • Test of cryogenic and long term operation • Energy resolution (expected 1.4 – 2 %) • Position resolution (few mm) • Timing resolution (100 ps) • Measurement done with: • Cosmic rays • 40 MeV  from Compton Backscattering • -sources

  23. -source LEDs The LP from “inside” FRONT face -sources and LEDs used for PMT calibrations and monitoring

  24. Gain • Masurements of light from LEDs: 2 =g ( q – q0 ) + 02 • Absolute knowledge of the GAIN of ALL PMTs within few percents  On the gain knowledge (including syst.) (2  1) % PMT with problems

  25. QE Quantum efficiencies measurement With -source in 170 K GXe …to be performed better, a dedicated measurement station

  26. Daily measurement of PMT gain 30 days

  27. First tests showed that the observed number of scintillation photons is MUCH LESS than expected • It improved with every liquefaction/recovery cycle • Looks like there is some absorption due to contaminants abs 7 cm

  28. Contamination? A comparison with H2O and O2 absorption spectra shows that the presence of such molecules at ppm level seriously affect Xe transparency Confirmed by mass-spectrometry measurements

  29. O2 absorption

  30. Purification • Before operation: circulation with HOT GXe • A circulation + purification system has been introduced (oxysorb + SAES getter) guaranteed to < 1 ppb for H2O and O2 • Recondensation with refrigerator + liquid nitrogen

  31. Light increase on PMTs (-source) A factor of 30! Near PMTs (d = 7 – 11 cm ) Far PMTs (d = 40 cm) L  exp(-d/abs)

  32. Improvement in Light Yield for  Front Mid Back

  33. A  seen by the LP

  34. Increase of light with time

  35. Improvement with time We see an improvement both in comparison with MC simulation and GXe data No Monte Carlo !! Increase with time

  36. Measurement of relative and abslolute light yield • Limit on the absorption length preliminary LY = 34000 ph/MeV abs > 100 cm @ 95 % C.L.

  37. MC Prediction

  38. Rayleigh scattering measurement 30 cm 45 cm 60 cm

  39. Cosmic rays Cosmic rays data are in agreement with data from -sources MC light yield corrected with that measured for -sources LY() = 0.8 * LY() preliminary …Purification still in progress

  40. LoI now Proposal Planning R & D Assembly Data Taking 1997 1998 1999 2000 2001 2002 2003 2004 2005 Summary and Time Scale • All sub-detectors within time scale • Near future: • Test beam of Large Prototype for E, position and timing with clean Xe • -Transport system test Further interest http://meg.psi.ch http://meg.icepp.s.u-tokyo.ac.jp http://meg.pi.infn.it

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