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 Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 1 Outline • • • • Physics motivation for a e experiment Quick look at the e decay The detector Recent progress Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 2 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 BR (μ eγ) 1015 1013 in SU(5) clear evidence for physics beyond the SM Exp. Bound J.Hisano et al.,Phys. Lett. B391 (1997) 341 R. Barbieri et al.,Nucl. Phys. B445(1995) 215 2 mτ SO(10) predicts even larger BR: SO(10) (μ eγ) SU (5) (μ eγ) 100 SU (5) (μ eγ) mμ Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 3 SO(10) SUSY-GUT Models R. Ciafaloni, A. Romanino, A. Strumia, Nucl. Phys. B458 (1996) Present Limit (MEGA) BRe < 1.2 10-11 Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 4 oscillations SU(5) with right-handed neutrinos Experimental Bound J. Hisano, N. Nomura, Phys. Rev. D59 (1999) Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 5 The MEG Collaboration INFN & Pisa University A. Baldini M. Grassi G. Signorelli C. Bemporad F. Cei D. Nicolò R. Pazzi F. Sergiampietri INFN & Pavia University A. De Bari P. Cattaneo G. Cecchet S. Mihara H. Nishiguchi T. Saeki T. Mitsuhashi W. Ootani R. Sawada A. Maki K. Yoshimura Y. Makida ICEPP, University of Tokyo T. Mashimo T. Mori K. Ozone S. Yamashita KEK, Tsukuba T. Haruyama A. Yamamoto Osaka University Y. Kuno Waseda University T. Doke S. Suzuki T. Yoshimura J. Kikuchi K. Terasawa H. Okada M. Yamashita BINP, Novosibirsk L. M. Barkov V. P. Smakhtin A. A. Grebenuk B. I. Khazin PSI, Villigen J. Egger P-R. Kettle S. Ritt Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 6 Experimental Search for e = back-to-back e E = 52.8 MeV E = 52.8 MeV •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 Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 7 Present Design Switzerland Drift Chamber, Beam Line, DAQ Russia LXe Tests and Purification Italy Japan e+ counter, Trigger, M.C. LXe Calorimeter, LXe Calorimeter Superconducting Solenoid, M.C. Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 8 Signal and Background “Signal” “Prompt” e e “Accidental” e e e e e ee e e Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 9 Sensitivity and Background Rate The sensitivity of the experiment is limited by accidental background BRacc R Ee E te ?~ 5 10 2 e 2 e 15 Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 10 Beam Transport System at PSI •Must provide continuous 108 /sec with few e+ contamination •Two separate configurations of the pE5 beam line, “U”-branch and “Z”branch (29 MeV/c ’s) Primary proton beam Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 11 U/Z-Branch Comparison Condition "Z"-branch "U"-branch No Degrader, Transmitted to Zone 3.6 · 108 +s-1 6.0 · 108 e+s-1 3.5 · 108 +s-1 1.6 · 109 e+s-1 Degrader, at Final Focus 2.0 · 108 +s-1 3.2 · 107 +s-1 9 16.5 /e ratio at Muon Peak 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 Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 12 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 Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 13 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 Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 14 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 Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 15 Drift Chamber 90Sr source Tokyo Univ. R 93 10m long 425 7 m (no magnetic field here test in PSI) Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 16 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 Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 17 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 Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 18 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 2103 s-1 •Design and simulation of type1 board completed interaction point (PMT of max charge) e+ hit point in timing counter time correlation – e+ angular correlation – e+ 200 s-1 20 s-1 •Prototype board delivered in Pisa by this fall Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 19 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 • See http://midas.psi.ch/mscb Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 20 Readout electronics •Waveform digitizing for all channels Prototypes delivered in autumn •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 Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 21 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 Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 22 The LP from “inside” -sources and LEDs used for PMT calibrations and monitoring LEDs -source Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 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 Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 25 QE Quantum efficiencies measurement With -source in 170 K GXe …to be performed better, a dedicated measurement station Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 26 Daily measurement of PMT gain 30 days Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 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 Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 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 Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 29 O2 absorption Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 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 Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 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) Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 32 Improvement in Light Yield for Front Mid Back Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 33 A seen by the LP Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 34 Increase of light with time Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 35 Improvement with time We see an improvement both in comparison with MC simulation and GXe data Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 36 •Measurement of relative and abslolute light yield •Limit on the absorption length LXe / GXe 2.6 0.3 meas. 3.0 0.1 Miyajima et al. LY = 34000 ph/MeV abs > 100 cm @ 95 % C.L. Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 37 MC Prediction Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 38 Rayleigh scattering measurement 30 cm 45 cm 60 cm Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 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() …Purification still in progress Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 40 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 LoI Planning 1997 now Proposal R&D 1998 1999 2000 2001 2002 Assembly Data Taking 2003 2005 2004 Further interest http://meg.psi.ch http://meg.icepp.s.u-tokyo.ac.jp http://meg.pi.infn.it Giovanni Signorelli, INFN Pisa and Scuola Normale Superiore. NUFACT 2002, London July, 1-6 2002 41