MEG Status and Prospects

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MEG Status and Prospects

• Toshiyuki Iwamoto
• Paul Scherrer Institute

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Physics

• m ? e g
• Lepton flavor violating process
• Clear evidence of new physics beyond SM
• Explore SUSY-GUT/seesaw
• Current Experimental limit
• MEGA Br(m-gteg) 1.2x10-11
• MEG sensitivity Br(m-gteg) 10-13

10-11
MEGA
10-13
MEG
J. Hisano and D. Nomura, 1998
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Sensitivity

• Signal
• clear two body decay
• Background
• Radiative m decay
• m ? e nm ne g lt 10-14
• Accidental overlap
• m ? e n n random g 10-14
• To reject these background,
• energy, timing and vertex resolution
• pile-up rejection from waveform analysis

Signal event
Radiative decays
Accidental
Detector resolution
Sensitivity
DEg 5 DEe 0.9 dteg 100ps dqeg 23mrad
m beam rate 0.3x108/s Measurement time 2
years Background event 0.5 Br(m-gteg) lt
1.5x10-13
dominant
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Detector
Approved in 1999 at PSI in Switzerland, Physics
run in 2007 Japan, Italy, Switzerland, Russia,
and USA collaboration
e COBRA spectrometer g liquid xenon detector
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Detector
Drift chamber
590 MeV proton Ring Cyclotron
COBRA magnet w/ graded B field
Photon detector
Timing counter
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Beam Line
PSI Proton Cyclotron 590MeV, gt1.8mA Most intense
DC beam 108 m/s accidental coincidence is
dominant ? lower m rate is better ? DC
beam surface muon beam 28MeV/c m to
avoid capture inside stopping target Beam spot
size 11mm at target
28MeV/c
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COBRA Spectrometer
Compensation coil
Constant Bending Radius spectrometer
Gradient magnetic field, 1.27T at z 0, I 360A
I 200A
COBRA magnet
Photon detector lt 50G
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Drift Chamber
16 chambers arranged radially with
10interval Position resolution 300mm for both
r and z Momentum resolution 0.4 Low material
(multiple scattering suppression)
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Drift chamber design
z
r
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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-measurement
• Obtained goal st 40ps (100ps FWHM)

z
f
Exp.Application Size(cm) Scinti. PMT L(att)cm s(meas) s(exp)
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
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Xenon detector
900l liquid xenon 846 2 PMT directly into
Liquid Scintillation only high light output,
fast response ?
good resolution Energy, position and timing of g
measured Waveform digitization ? to reject
pile-up events RD low temperature (160K), VUV
light, H2O purification, and
performance test by 70 liter size
prototype
g
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PMT
Total 14.2MW
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
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Purification

• Gas Liquid phase purification tested
• Metal getter (zirconium) by gas 0.5l/h
• Molecular sieves by liquid 100l/h

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Xenon detector performance
83MeV
p- (at rest) p -gt p0 n, p0(28MeV/c) -gt g
g 55, 83MeV monochromatic energy calibration
H2 target
Prototype LXe
55MeV
LYSO
g
g
NaI
p-
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Xenon detector performance
Energy distribution _at_ 55MeV

• 1.23 0.09
• FWHM4.8

Timing distribution
110 psec
Expected Performance Energy 5 (FWHM)
Timing 150 psec (FWHM) Vertex 9mm (FWHM)
110 - 64 (LYSO) - 61 (Beam) 65psec
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Liquid xenon system
Liquid xenon detector
gas purifier
Refrigerator
Liquid purifier
250l gas xenon tank x 8
1000l liquid xenon storage tank
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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
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Calibration method

• Gain monitor LED
• Q.E. 241Am a source
• Energy
• 55, 83, and 129 MeV g from p-p?p0n, p0?2g
• Ni thermal neutron capture 9MeV
• Proton accelerator
• Li(p,?)Be 17.6MeV
• resonant at Ep 440 keV ?14 keV ?peak 5
  mb

3x3 NaI array
9 MeV Nickel g-line
17.6 MeV Li(p,g)Be-line
LH2 target
55, 83, and 129 MeV g
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Positron spectrometer commissioning run in 2006

• Beam
• COBRA spectrometer
• DAQ/Trigger
• LXe detector not ready

Drift chamber
Timing counter
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Commissioning run result

• Beam
• 108 m/s confirmed
• Spot size sx sy 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

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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
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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

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END