meg experiment at psi r&d of liquid xenon photon detector
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Satoshi Mihara, Frontier Detectors for Frontier Physics, La Biodola, Isola d'Elba May 2003
R&D work on a Liquid XenonDetector for the e Experiment at PSI
on behalf of the MEG Collaboration
University of Tokyo, Japan Presented by S. Mihara
http://meg.psi.ch
I. MEG Experiment at PSI
II. R&D of Liquid Xenon Photon Detector
Satoshi Mihara, Frontier Detectors for Frontier Physics, La Biodola, Isola d'Elba May 2003
• Neutrino Oscillation + SUSY– Hisano and Nomura 1998
e e Search as Search asFrontier PhysicsFrontier Physics
Solar Neutrino
tan
SK+SNO etc.=Large Mixing SolutionSK+SNO etc.=Large Mixing Solution
Current limitby MEGA
• e in…– SM+Neutrino Oscillation
• Suppressed as (∝ m/mW)4
– SUSY• Large top Yukawa coupling
e
e~ ~
~
W e
e
MR(GeV)
Br(
e)
10-10
10-11
10-12
10-13
10-14
10-15
Satoshi Mihara, Frontier Detectors for Frontier Physics, La Biodola, Isola d'Elba May 2003
MEG Experiment OverviewMEG Experiment Overview
• Detect e+ and , “back to back” and “in time”
• 100% duty factor continuous beam of ~ 108/sec
– better than pulsed beam to reduce pile-up events
• Two characteristic components
1. Liquid Xe photon detector
2. Solenoidal magnetic spectrometer with a graded magnetic field (COBRA)
Satoshi Mihara, Frontier Detectors for Frontier Physics, La Biodola, Isola d'Elba May 2003
Signal and BackgroundSignal and Background
• Signal• Main background sources
– Radiative + decay• If neutrinos carry small amount of
energy, the positron and gamma can mimic the signal.
– Accidental overlap• A positron from usual Michel decay
with energy of half of m
• Gamma from– Radiative muon decay or– Annihilation in flight of positron
NOT back to back, NOT in time e
e+””
?
enn
e
Ee = 52.8 MeV
Signal e= 180°
Eg = 52.8 MeV
e
Satoshi Mihara, Frontier Detectors for Frontier Physics, La Biodola, Isola d'Elba May 2003
Requirement onRequirement onthe Photon Detectorthe Photon Detector
• Good resolutions– Energy– Position– Time
• Large acceptance with good uniformity
• Fast decay time to reduce pile-up events
Satoshi Mihara, Frontier Detectors for Frontier Physics, La Biodola, Isola d'Elba May 2003
Properties of XenonProperties of Xenon
Fast response, Good Energy, and Position resolutions Wph = 24 eV
(c.f. Wph(NaI) = 17eV) tfast =4.2nsec tslow=22nsec
Narrow temperature range between liquid and solid phases Stable temperature control
with a pulse-tube refrigerator
Property Unit
Saturated temperature T(K) 164.78
Saturated pressure P(MPa) 0.100
Latent heat (for liquid) (J/kg)X103 95.8
Latent heat (for solid) '(J/kg)X103 1.2
Specific heat Cp(J/kgK)X103 0.3484
Density (kg/m3)X103 2.947
Thermal conductivity (W/mK) 0.108
Viscosity (Pa-s)X10-4 5.08
Surface tension (N/m)X10-3 18.46
Expansion coefficient (1/K)X10-3 2.43
Temperature/Pressure at triple point Tt(K)/PT(MPa) 161.36/0.0815
Satoshi Mihara, Frontier Detectors for Frontier Physics, La Biodola, Isola d'Elba May 2003
Liquid XenonLiquid XenonPhoton DetectorPhoton Detector
3 cm
Liq. Xe
Liq. Xe
14 cm
(a)
(b)
05 10 15
2025
3035
0
10
20
30
40
50
0
2000
4000
6000
8000
10000
05
1015 20 25
3035
0
10
20
30
40
50
0
200
400
600
800
1000
1200
1400
1600
1800
52.8 MeV
52.8 MeV
800 liter LXe viewedby ~ 800PMTs
800 liter LXe viewedby ~ 800PMTs
Shallow event
Deep event
Satoshi Mihara, Frontier Detectors for Frontier Physics, La Biodola, Isola d'Elba May 2003
Absorption of Scintillation LightAbsorption of Scintillation Light• Scintillation light emission from an excited molecule
– Xe+Xe*Xe2*2Xe + h
• Water contamination absorbs scintillation light more strongly than oxygen. abs=7cm
abs=500cm
Depth
Dep
th p
aram
eter
Dep
th p
aram
eter
SimulationFor Large Prototype
Satoshi Mihara, Frontier Detectors for Frontier Physics, La Biodola, Isola d'Elba May 2003
• Small Prototype done • Proof-of-Principle Experiment• 2.3liter active volume
• Large Prototype in progress• Establish operation technique• 70 liter active volume
• Final Detector starting• ~800 liter
R&D StrategyR&D Strategy
Satoshi Mihara, Frontier Detectors for Frontier Physics, La Biodola, Isola d'Elba May 2003
Small PrototypeSmall Prototype• 32 2-inch PMTs surround the
active volume of 2.34 liter
• -ray sources of Cr,Cs,Mn, and Y
• source for PMT calibration
• Operating conditions– Cooling & liquefaction using
liquid nitrogen
– Pressure controlled
– PMT operation of 1.0x106 gain
•Proof-of-Principle Experiment
•PMT works in liquid xenon?
•Light yield estimation is correct?
•Simple setup to simulate and easy to understand.
•Proof-of-Principle Experiment
•PMT works in liquid xenon?
•Light yield estimation is correct?
•Simple setup to simulate and easy to understand.S.Mihara et al. IEEE TNS 49:588-591, 2002
S.Mihara et al. IEEE TNS 49:588-591, 2002
Satoshi Mihara, Frontier Detectors for Frontier Physics, La Biodola, Isola d'Elba May 2003
Small PrototypeSmall PrototypeEnergy resolutionEnergy resolution
• Results are compared with MC prediction.1. Simulation of int. and energy
deposition : EGS4
2. Simulation of the propagation of scint. Light
EGS cut off energy : 1keV
Rayleigh Scattering Length: 29cm
Wph = 24eV
Satoshi Mihara, Frontier Detectors for Frontier Physics, La Biodola, Isola d'Elba May 2003
Small PrototypeSmall PrototypePosition and Timing resolutionsPosition and Timing resolutions
• PMTs are divided into two groups by the y-z plane
– g int. positions are calculated in each group and then compared with each other.
– Position resolution is estimated as
sz1-z2/√2
• The time resolutionis estimated bytaking the difference
between two groups. • Resolution improves
as ~ 1/√Npe
•
Satoshi Mihara, Frontier Detectors for Frontier Physics, La Biodola, Isola d'Elba May 2003
Large PrototypeLarge Prototype• 70 liter active volume (120 liter
LXe in use)• Development of purification
system for xenon• Total system check in a
realistic operating condition:– Monitoring/controlling systems
• Sensors, liquid N2 flow control, refrigerator operation, etc.
– Components such as• Feedthrough,support structure
for the PMTs, HV/signal connectors etc.
– PMT long term operation at low temperature
• Performance test using– 10, 20, 40MeV Compton beam– 60MeV Electron beam
Satoshi Mihara, Frontier Detectors for Frontier Physics, La Biodola, Isola d'Elba May 2003
Purification SystemPurification System• Xenon extracted from the
chamber is purified by passing through the getter.
• Purified xenon is returned to the chamber and liquefied again.
• Circulation speed 5-6cc/minute
• Enomoto Micro Pump MX-808ST-S– 25 liter/m
– Teflon, SUS
Gas return
To purifier
Circulation pump
Satoshi Mihara, Frontier Detectors for Frontier Physics, La Biodola, Isola d'Elba May 2003
Purification PerformancePurification Performance
• 3 sets of Cosmic-ray trigger counters
• 241Am alpha sources on the PMT holder
• Stable detector operation for more than 1200 hours
Cosmic-ray events events
Satoshi Mihara, Frontier Detectors for Frontier Physics, La Biodola, Isola d'Elba May 2003
Absorption LengthAbsorption Length
• Fit the data with a function :
A exp(-x/ abs)
• abs >100cm (95% C.L) from comparison with MC.
• CR data indicate that abs > 100cm has been achieved after purification.
Satoshi Mihara, Frontier Detectors for Frontier Physics, La Biodola, Isola d'Elba May 2003
Response to Gamma Beam Response to Gamma Beam
10MeV
20MeV40MeV
• Electron storage ring,
TERAS, in AIST,
Tsukuba Japan
• Electron Energy, Current:762MeV, 200mA
• 266nm laser to induce inverse-Compston scattering.
• 40 MeV (20MeV, and 10MeV) Compton provided.
• The Compton edge is used to evaluate the resolution.
• Data taking– Feb. 2002 (w/o purification)
– Apr. 2003 (w/ purification)
Satoshi Mihara, Frontier Detectors for Frontier Physics, La Biodola, Isola d'Elba May 2003
Energy SpectrumEnergy Spectrum• 2 :depth parameter:
40MeV Compton gamma dataw/ xenon purification
40MeV Compton gamma dataw/o xenon purification
Dep
th p
aram
eter
Dep
th p
aram
eter
Total Number of Photoelectrons Total Number of Photoelectrons
Satoshi Mihara, Frontier Detectors for Frontier Physics, La Biodola, Isola d'Elba May 2003
Energy ResolutionEnergy Resolution• Shallow events have dependence on the depth of the 1st
int. point.• Discard these shallow events (~34%) for quick analysis.• Calibration not completed• Very Preliminary: E < 2%
Dep
th p
aram
eter
Very Prel
iminary
Simulation
52.8MeV
Simulation
52.8MeV
Satoshi Mihara, Frontier Detectors for Frontier Physics, La Biodola, Isola d'Elba May 2003
Position ReconstructionPosition Reconstruction• 2-step reconstruction
– 1st step: Pre-determination of the peak
– 2nd step: Precise determination with an iteration process
• Data 40MeV Compton
(a) (b)
(c) (d)
Satoshi Mihara, Frontier Detectors for Frontier Physics, La Biodola, Isola d'Elba May 2003
Timing ResolutionTiming Resolution• Estimated using Electron Beam
(60MeV) data
• Resolution improves in proportion to 1/sqrt(Npe).
• For 52.8 MeV ~ psec + depth resolution.
• QE improvement and wave-form analysis will help to achieve better resolution.
(Visit “The DRS chip” by S.Ritt)
T
imin
g R
esol
utio
n (p
sec)
104 4x104
45 MeV Energy deposit by 60 MeV electron injection
52.8MeV
(nsec)
=75.62.0ps=75.62.0ps
Number of Photoelectron
Satoshi Mihara, Frontier Detectors for Frontier Physics, La Biodola, Isola d'Elba May 2003
SummarySummary
• New experiment to search for e at Paul Scherrer Institut• Two characteristic components (and many others)
– Liquid Xenon Photon Detector– Solenoidal magnetic spectrometer with a graded magnetic field
(COBRA)
• R&D of liquid xenon photon detector using the large prototype– Long term stable operation using a pulse tube refrigerator– Purification of liquid xenon – Very preliminary result from the last beam test
• E<2% for 40MeV Compton
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