Transcript Document
Liquid Xenon Detector for the MEG Experiment Toshiyuki Iwamoto 4/Oct/2006 10th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD06) Siena 4/Oct/2006 Siena 2006 1 MEG Physics • Lepton flavor violating process – already violated in neutrino sector • Forbidden in the Standard Model • Sensitive to the new physics models, SUSY GUT, or SUSY seesaw etc. Clear 2-body kinematics Ee = Eg = 52.8 MeV Back to back (qeg = 180°) Simultaneous (Te = Tg) • The present experimental limit – ~ 1.2x10-11 by MEGA experiment 4/Oct/2006 Siena 2006 2 Sensitivity Background Radiative m decay : m+ e+ nm ne g < 10-14 Accidental overlap: m decay m e n n + random g To reject these background, energy, timing and vertex resolution pile-up rejection from waveform analysis Single event sensitivity ~ 4x10-14 Background event ~ 4x10-14 90% C.L. sensitivity ~ 1x10-13 MEGA photon detector requirement DEg = 5% (FWHM) DTg = 150ps (FWHM) DXg = 9mm (FWHM) 4/Oct/2006 MEG Siena 2006 3 MEG detector Approved in 1999 at PSI Physics run in 2007 4/Oct/2006 Siena 2006 4 MEG Detector 590 MeV proton Ring Cyclotron Drift chamber COBRA magnet w/ graded B field Most intense DC muon beam (108/s) H. Nishiguchi, 5th Oct “The MEG positron spectrometer” 4/Oct/2006 Photon detector Siena 2006 Timing counter 5 Photon Detector 800 liter liquid xenon, 846 2” PMTs in liquid High light yield, fast response and good uniformity (~40000ph/MeV, t=4.2, 22, 45ns) Low temperature (~160K), l = 178nm : development of PMT, refrigerator Xenon purity : remove H2O Performance test of Xe detector 2.3 liter prototype confirmed the principle of Xe 68.6 liter prototype 10, 20, and 40 MeV inverse Compton scattering g energy, timing and vertex resolution 55, 83MeV, 129MeV g from p-p->np0,ng reaction energy, and timing resolution 4/Oct/2006 Siena 2006 6 Improvement PMT Q.E. : ~15% Photocathode : K-Cs-Sb Metal channel dynode, 12 stages Silica window (for UV light) Purification Gas & Liquid phase purification tested Metal getter (zirconium) by gas ~0.5l/h Molecular sieves by liquid ~100l/h Compact, and low heat load Tolerance up to 100G magnetic field Al strip to keep surface resistance at low temp. Zener diode for high rate background 1m 57mm 4/Oct/2006 2.5m Siena 2006 7 Prototype test, 10~40MeV g 68.6l liquid xenon prototype detector 228 PMTs 40MeV g Energy s ~ 4mm 1.6% in s 4/Oct/2006 Siena 2006 Vertex distribution 8 H2 target g g LYSO NaI pm p- (at rest) + p -> p0 + n, p0(28MeV/c) -> g + g (54.9MeV<Eg<82.9MeV) Almost monochromatic g is available p- + p -> n + g (129MeV) Energy, timing resolution neutron response 4/Oct/2006 83MeV 175° 170° 55MeV Opening angle (q) phe Xenon detector Prototype LXe Energy (MeV) Prototype test, 55~129MeV g Siena 2006 9 ENaI + ELYSO (MeV) Energy distribution @ 55MeV s= 1.23 ±0.09 % FWHM=4.8 % Timing distribution Energy Resolution (s) [%] Photon detector performance 5% Energy resolution vs. Energy 1% 110 psec 110 - 64 (LYSO) - 61 (Beam) = 65psec 4/Oct/2006 Siena 2006 Expected Performance Energy : 5% (FWHM) Timing : 150 psec (FWHM) Vertex : 9mm (FWHM) 10 Detector operation 250l gas xenon tank x 8 GXe pump (10-50L/min) purifier Heat exchanger GXe storage tank Getter+Oxysorb Cryocooler (100W) LN2 Refrigerator LN2 Cryocooler (150W) Liquid pump (100L/h) Purifier 4/Oct/2006 LXe Calorimeter Liquid circulating purifier Siena 2006 1000L storage dewar 1000l liquid xenon storage tank 11 Calibration method • Gain monitor : LED • Q.E. : 241Am a source • Energy 3x3 NaI array – 55, 83, and 129 MeV g from p-pp0n, p02g – Ni thermal n capture 9MeV – Proton accelerator • Li(p,g)Be 17.6MeV • B(p,g)C 16.1MeV • Timing – Laser – radiative m decay – 55 MeV g from p-pp0n reaction (Pb+Scintillator) LH2 target • Vertex – 55 MeV g from p-pp0n reaction (collimator) 4/Oct/2006 Siena 2006 12 Detector Construction 4/Oct/2006 Siena 2006 13 Detector Construction top outer side inner The performance of all PMTs checked in the liquid xenon before installation 4/Oct/2006 Siena 2006 14 Schedule • Cryostat will come to PSI in the end of this year • PMT installation into holders almost done • Liquid xenon detector assembly will be done in the beginning of next year, and then liquefaction, purification and stable operation test will be continued. • physics run starts in 2007 • Positron spectrometer run and calibration run will be done in this year 4/Oct/2006 Siena 2006 15 Summary • MEG experiment will search for m->eg with better sensitivity than previous experiment • The performance of liquid xenon detector has been tested by using prototype, and the real detector is being constructed • Physics run of MEG experiment will start in 2007. • Positron spectrometer data and calibration data will be taken in this year. 4/Oct/2006 Siena 2006 16