MEG 実験 2009 液体キセノン検出器の性能 II 西村康宏, 他 MEG...
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MEG 実験 2009液体キセノン検出器の性能 II
西村康宏 , 他 MEG コラボレーション
東京大学素粒子物理国際研究センター
第 65 回年次大会 岡山大学
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Contents
• Monitoring the liquid xenon (LXe) detector during physics data taking– Light yield– Detector gain
• Performance in 2009– Energy– Position– Detection efficiency
2010/3/23 日本物理学会 第65回年次大会 岡山大学津島キャンパス 2
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LXe detector
protonmuon
beam line
Monitoring tools of LXe detector• Cockcroft-Walton accelerator
– Nuclear reaction by protons– Li(p, )Be 14.6, 17.6MeV– B(p, )C 4.4, 11.7MeV– Useful to monitor the light yield and
to check the uniformity of detector response
• LED, 241Am source and cosmic ray– Monitor in both beam on and off
• PMT gain affected by beam current, which is corrected but to be confirmed.
– Alpha events triggered even in + beam since 2009• - separation improved by the change of the scintillation property
• Checked the stability of the light yield and of the detector gain
2010/3/23 日本物理学会 第65回年次大会 岡山大学津島キャンパス 3
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Monitoring light yield• Reached full intensity in 2009• Purification finished before 2009
physics run• Checked the stability of the light yield
– Use 17.6MeV Li peak by CW accelerator (3times / week)
2010/3/23 日本物理学会 第65回年次大会 岡山大学津島キャンパス 4
1%
2009
2008
• Stable within ~1% during physics run in 2009
The light yield history in 2009 by Li 17.6MeV
The light-yield history 2008-2009Li 17.6MeVCosmic ray
Li 17.6MeV peak
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Monitoring the detector in beam• The light yield was stable but PMT gain shifted with + beam
• The shift is measured using LED and it's corrected depending on beam status• We confirmed that the detector was stable
by monitoring LED, , cosmic ray
2010/3/23 日本物理学会 第65回年次大会 岡山大学津島キャンパス 5
• Stable within the precision of each monitoring
from 241Am Cosmic rayLED
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Energy reconstruction• Energy
• The number of scintillation photons = (weight x PMT charge / gain / Q.E.) x energy scale x correction factor
• Energy scale determined at 55MeV in 0 run near signal 53MeV ray• Correction factor for the change of the light yield and non-uniformity
• The light yield was stable so not used in 2009• Non-uniformity of the scintillation-photons detection measured by Li peak
– Intrinsic non-uniformity exists due to the current reconstruction method– Observed the change with light yield increased in 2008– Non-uniformity differs from 2008 results after light yield completely increased– Make correction factor for 2009 run
2010/3/23 日本物理学会 第65回年次大会 岡山大学津島キャンパス 6
17.6
MeV
pea
k [a
.u.]
• Uniformity within 0.14% after correction
0.14% CW w/o correction
CW (corrected)Uniformity before/after correctionDetector
inner face
Peak [a.u.]
• Non-uniformity measured by 17.6MeV
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Energy resolution around signal E• 55MeV from 0 decay
– Gaussian for upper partand exponential for a lower tail
2010/3/23 日本物理学会 第65回年次大会 岡山大学津島キャンパス 7
Preliminary
distribution on inner face
Detector inner face
upper
along depth from inner face
Energy resolution in at 55MeV
• 2.0% upper (averaged)– The same result as 2008 even
after the light yield improved.
Events along depth
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Energy linearity / resolution• Checked linearity and energy resolution by various energies
– B (4.4MeV, 12.0MeV), Li (17.6MeV), 0 decay (54.9MeV, 83.0MeV), - p → n (129MeV)
2010/3/23 日本物理学会 第65回年次大会 岡山大学津島キャンパス 8
CEX
CW
AmBe
determination determination of energy scaleof energy scale
CEX
CW
pedestalPrelim
inary Preliminary
• Enable the extrapolation to signal 53MeV region
Signal
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Position measurement• Reconstruct position by the light distribution
on inner face• Position resolution in 2009 was measured
with a new lead collimator– Long slits along the beam axis are prepared
– Estimate a bias of absolute position on a long line – 1cm and 5mm slits with 1.8cm thickness are prepared
– Put in front of the detector in 0 run
2010/3/23 日本物理学会 第65回年次大会 岡山大学津島キャンパス 9
Detectorinner face
Scanning peaks along beam axis
PMT
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1cm slitPea
k po
sitio
nPerformance of position reconstruction
• Position determination : 0.7mm bias– Enough small compared with resolution
2010/3/23 日本物理学会 第65回年次大会 岡山大学津島キャンパス 10
Wid
th o
f pea
k
1cm slit
5mm slit
• Averaged width of peaks 10mm slit : 6.8mm , 5mm slit : 6.4mm • Position resolution is the same as in 2008 : 5mm
– Obtained after subtracting effects of projected slits size and beam spread of ~ 8mm excluded
Central 1cm slit
All slits
Central 1cm slit
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Detection efficiency• Lower energy tail of energy distribution is taken into account
– Interaction with material before reaches acceptance of LXe detector– Leakage of photons near the detector's face
• Absolute detection efficiency obtained from Monte Carlo simulation– Signal with position dependence : 67% (E > 46MeV)
• Consistency check by 0→2 between measurement and MC– Counts coincident 2 decay in LXe detector tagged by the NaI– Set energy region, no analysis cut– 67% in 2009 with twice amount of data in 2008
• Consistent with 66% in 2008– 4% difference between data and MC
2010/3/23 日本物理学会 第65回年次大会 岡山大学津島キャンパス 11
data
MC
Neutron from -p→n is subtracted
Preliminary
? 83MeV
55MeV
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Conclusions
• Checked the stable operation during physics data taking in 2009
• Performance in 2009 with the increased light yield and upgraded waveform digitizer is almost the same as 2008 result (preliminary)
– Energy resolution to be 2.0% average– 67ps LXe timing and 180ps of -e+ timing in previous talk– 5mm with 0.7mm bias of reconstructed position
• 67% detection efficiency in 0 run is consistent with 2008
• Investigating more proper calibration and analysis
2010/3/23 日本物理学会 第65回年次大会 岡山大学津島キャンパス 12