MEG Status and Prospects Toshiyuki Iwamoto Paul Scherrer Institute - - PowerPoint PPT Presentation
MEG Status and Prospects Toshiyuki Iwamoto Paul Scherrer Institute Physics e Lepton flavor violating process Clear evidence of new physics beyond SM Explore SUSY-GUT/seesaw Current Experimental limit 10 -11
Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 2
µ e γ
– Lepton flavor violating process – Clear evidence of new physics beyond SM – Explore SUSY-GUT/seesaw
Current Experimental limit
– MEGA Br(µ−>eγ) ~ 1.2x10-11
MEG sensitivity Br(µ−>eγ) ~ 10-13
MEGA MEG 10-11 10-13
Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 3
Signal
– clear two body decay
Background
– Radiative µ decay : µ+ e+ νµ νe γ < 10-14 – Accidental overlap: µ e ν ν + random γ ~ 10-14
To reject these background,
– energy, timing and vertex resolution – pile-up rejection from waveform analysis
Radiative decays Accidental
dominant
Signal event
µ+ e+ γ
180° 52.8MeV 52.8MeV
ΔEγ = 5% ΔEe = 0.9% δteγ = 100ps δθeγ= 23mrad
e+ γ ν ν µ+ µ+ e+ ν ν γ ?
µ+ beam rate : 0.3x108/s Measurement time : 2 years Background event : 0.5 Br(µ->eγ) < 1.5x10-13
Detector resolution Sensitivity
Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 4
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 5
590 MeV proton Ring Cyclotron COBRA magnet w/ graded B field Photon detector Drift chamber Timing counter
Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 6
PSI Proton Cyclotron 590MeV, >1.8mA Most intense DC beam ~108 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 7
Constant Bending Radius spectrometer
Photon detector < 50G
Gradient magnetic field, 1.27T at z = 0, I = 360A
I = 200A Compensation coil COBRA magnet
Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 8
16 chambers arranged radially with 10°interval Position resolution ~ 300µm 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 9
r z
Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 10
43 38 270 R5924 BC404 4x4x90 MEG 143 90 250 R6680 BC408 4x6x255 Belle 420 180 180 XP2020 SCSN38 2x3x300 R.Stroynowski 240 210 300 R1828 BC412 4.2x13x400 TOPAZ 137 110 270 XP2020 BC408 5x10x280 R.T.Gile 53 50 200 R1828 SCSN23 4x3.5x100 T.Sugitate 110 140 180 R1332 SCSN38 3x20x150 T.Tanimori 60 120 200 XP2020 NE114 3x15x100 G.D.Agastini σ(exp) σ(meas) L(att)cm PMT Scinti. Size(cm) Exp.Application
Outer layer, plastic scintillator read out by PMTs: timing measurement Inner layer, scintillation fiber read out with APDs: z-measurement
φ z
Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 11
900l liquid xenon 846 2” PMT directly into Liquid Scintillation only : high light output, fast response good resolution Energy, position and timing of γ measured Waveform digitization to reject pile-up events R&D : low temperature (160K), VUV light, H2O purification, and performance test by 70 liter size prototype
γ
Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 12
Total : 14.2MΩ
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 13
– Metal getter (zirconium) by gas ~0.5l/h – Molecular sieves by liquid ~100l/h
Before purification After purification
2.5m 1m
Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 14
Opening angle (θ) Energy (MeV)
π- (at rest) + p -> π0 + n, π0(28MeV/c) -> γ + + γ 55, 83MeV monochromatic energy calibration
55MeV 83MeV
Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 15
110 - 64 (LYSO) - 61 (Beam) = 65psec
110 psec σ= 1.23 ±0.09 % FWHM=4.8 %
Expected Performance Energy : 5% (FWHM) Timing : 150 psec (FWHM) Vertex : 9mm (FWHM) 5% 1% Energy Resolution (σ) [%] Energy resolution vs. Energy Energy distribution @ 55MeV Timing distribution
Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 16
Refrigerator 1000l liquid xenon storage tank 250l gas xenon tank x 8 Liquid purifier gas purifier Liquid xenon detector
Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 17
The performance of all PMTs checked in the liquid xenon before installation After PMT installation into holders, HV set on for all PMTs
side top inner
Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 18
– 55, 83, and 129 MeV γ from π-pπ0n, π02γ – Ni thermal neutron capture 9MeV – Proton accelerator
resonant at Ep= 440 keV Γ=14 keV σpeak = 5 mb
3x3 NaI array LH2 target 9 MeV Nickel γ-line 17.6 MeV Li(p,γ)Be-line 55, 83, and 129 MeV γ
Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 19
Timing counter Drift chamber
Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 20
– 108 µ+/s confirmed – Spot size σx ~ σy ~ 11mm on target
– 8 of 16 chambers available – Successfully operated at highest intensity
– Full counters without z-measuring fiber counter
– Trigger electronics worked – DRS waveform data taken – Online DAQ software also worked
Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 21
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
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Toshiyuki Iwamoto, The 6th KEK Topical Conference, 6~8 Feb. 2007 23