MEG Status and Prospects Toshiyuki Iwamoto Paul Scherrer Institute - PowerPoint PPT Presentation

MEG Status and Prospects Toshiyuki Iwamoto Paul Scherrer Institute

Physics  µ  e γ – Lepton flavor violating process – Clear evidence of new physics beyond SM – Explore SUSY-GUT/seesaw  Current Experimental limit 10 -11 MEGA Br (µ − > e γ ) ~ 1.2x10 -11 – MEGA  MEG sensitivity Br (µ − > e γ ) ~ 10 -13 10 -13 MEG J. Hisano and D. Nomura, 1998 Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 2

Sensitivity  Signal Signal event e + – clear two body decay µ + Radiative decays 52.8MeV  Background e + γ ν µ + Radiative µ decay : – µ +  e + ν µ ν e γ < 10 -14 52.8MeV 180° γ – Accidental overlap: ν µ  e ν ν + random γ ~ 10 -14  To reject these background, – energy, timing and vertex resolution Accidental – pile-up rejection from waveform analysis ? Detector resolution Sensitivity e + γ µ + µ + beam rate : 0.3x10 8 /s Δ E γ = 5% Δ Ee = 0.9% Measurement time : 2 years ν δ t e γ = 100ps Background event : 0.5 ν Br ( µ -> e γ ) < 1.5x10 -13 δθ e γ = 23mrad dominant Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 3

Detector Approved in 1999 at PSI in Switzerland, Physics run in 2007 Japan, Italy, Switzerland, Russia, and USA collaboration e + : COBRA spectrometer γ : liquid xenon detector Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 4

Detector Drift chamber 590 MeV proton Ring Cyclotron COBRA magnet w/ graded B field Photon detector Timing counter Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 5

Beam Line PSI Proton Cyclotron 590MeV, >1.8mA Most intense DC beam ~10 8 µ /s accidental coincidence is dominant  lower µ rate is better  DC beam surface muon beam ~ 28MeV/c µ + to avoid capture inside stopping target Beam spot size ~11mm at target 28MeV/c Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 6

COBRA Spectrometer Compensation coil Constant Bending Radius spectrometer Gradient magnetic field, 1.27T at z = 0, I = 360A I = 200A COBRA magnet Photon detector < 50G Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 7

Drift Chamber 16 chambers arranged radially with 10°interval Position resolution ~ 300 µ m for both r and z Momentum resolution ~ 0.4% Low material (multiple scattering suppression) Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 8

Drift chamber design z r Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 9

Timing Counter •Two layers of scintillators: Outer layer, plastic scintillator read out by PMTs: timing measurement Inner layer, scintillation fiber read out with APDs: z z-measurement •Obtained goal σ t ~40ps (100ps FWHM) φ σ (meas) σ (exp) Exp.Application Size(cm) Scinti. PMT L(att)cm G.D.Agastini 3x15x100 NE114 XP2020 200 120 60 T.Tanimori 3x20x150 SCSN38 R1332 180 140 110 T.Sugitate 4x3.5x100 SCSN23 R1828 200 50 53 R.T.Gile 5x10x280 BC408 XP2020 270 110 137 TOPAZ 4.2x13x400 BC412 R1828 300 210 240 R.Stroynowski 2x3x300 SCSN38 XP2020 180 180 420 Belle 4x6x255 BC408 R6680 250 90 143 MEG 4x4x90 BC404 R5924 270 38 43 Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 10

Xenon detector 900l liquid xenon 846 2” PMT directly into Liquid Scintillation only : high light output, fast response  good resolution γ Energy, position and timing of γ measured Waveform digitization  to reject pile-up events R&D : low temperature (160K), VUV light, H 2 O purification, and performance test by 70 liter size prototype Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 11

PMT Total : 14.2M Ω Q.E. : ~15% Photocathode : K-Cs-Sb Metal channel dynode, 12 stages Silica window (for UV light) 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 Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 12

Purification • Gas & Liquid phase purification tested – Metal getter (zirconium) by gas ~0.5l/h – Molecular sieves by liquid ~100l/h After purification 1m 2.5m Before purification Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 13

Xenon detector performance 83MeV π - (at rest) + p -> π 0 + n, π 0 (28MeV/c) -> γ + + γ Energy (MeV) 55, 83MeV monochromatic energy calibration H 2 target Prototype 55MeV Opening angle ( θ ) LXe LYSO γ γ NaI π − Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 14

Xenon detector performance Energy distribution @ 55MeV Energy Resolution ( σ ) [%] 5% Energy resolution vs. Energy σ = 1.23 ±0.09 % FWHM=4.8 % 1% Timing distribution 110 psec Expected Performance Energy : 5% (FWHM) Timing : 150 psec (FWHM) Vertex : 9mm (FWHM) 110 - 64 (LYSO) - 61 (Beam) = 65psec Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 15

Liquid xenon system Liquid xenon gas purifier detector Refrigerator Liquid purifier 250l gas xenon tank x 8 1000l liquid xenon storage tank Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 16

Detector Construction (xenon) top outer side inner The performance of all PMTs checked in the liquid xenon before installation After PMT installation into holders, HV set on for all PMTs Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 17

Calibration method • Gain monitor : LED Q.E. : 241 Am α source • • Energy 55, 83, and 129 MeV γ from π - p  π 0 n , π 0  2 γ – – Ni thermal neutron capture 9MeV – Proton accelerator 3x3 • Li(p , γ ) Be 17.6MeV NaI array resonant at Ep= 440 keV Γ =14 keV σ peak = 5 mb 9 MeV Nickel γ -line 17.6 MeV Li(p, γ ) Be-line LH 2 target 55, 83, and 129 MeV γ Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 18

Positron spectrometer commissioning run in 2006 • Beam • COBRA spectrometer • DAQ/Trigger • LXe detector not ready Drift chamber Timing counter Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 19

Commissioning run result • Beam – 10 8 µ + /s confirmed – Spot size σ x ~ σ y ~ 11mm on target • DC – 8 of 16 chambers available – Successfully operated at highest intensity • TC – Full counters without z-measuring fiber counter • DAQ – Trigger electronics worked – DRS waveform data taken – Online DAQ software also worked Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 20

Plan for Year 2007 and After Run 2007 First half: complete beam tuning and COBRA spectrometer run Second half: start full MEG run as soon as calorimeter is ready Mid-2007 – 2009 MEG full DAQ 2010 – Detector upgrade / decay positron angular measurement Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 21

Summary • Physics run will start this year. • All detector components except for liquid xenon were installed and tested in the commissioning run at the end of last year. • A few months data will exceed MEGA limit • 2 years DAQ to reach 10 -13 sensitivity Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 22

END Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 23