Photon Detector Satoshi Mihara ICEPP, Univ. of Tokyo

1
Photon DetectorSatoshi Mihara ICEPP, Univ. of
Tokyo

• Large Prototype Study
• Gamma beam test
• Xenon purification
• Absorption length measurements
• Other related RD
• PMT development
• Purity monitor
• Final Photon Detector
• Expected performance (MC) ? Giovanni
• Calibration methods
• Cryogenics design ? Tom
• Schedule

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Gamma beam testg beam at TERASAnalysis
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40MeV Compton Gammaat TERAS

• Electron Energy762MeV.
• Max. current 200mA.
• 40 MeV (20MeV, and 10MeV) Compton g provided.
• Beam test in Feb. 2002 for 2 weeks

4
Energy Spectrum
40MeV Compton gamma data

• s2 depth parameter
• Correlation between s2 and Npe ? short labs as
  explained later
• In the region of 50lts2lt55 34.8(FWHM) including
  the energy spread of Compton g

34.8
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Comparison with MC with absorption

• Strong correlation between the s2 and Npe can be
  explained by introducing absorption effect into
  MC.
• MC with 7cm labs can explain the data.
• According to MC, labs longer than 1m is necessary
  to achieve the resolution of a few order.

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PositionResolution

• MC with labs10cm

• Data 40MeV Compton g

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Comparison with MC

• MC
• labs5,10,100,8 cm
• labs30cm
• Obtained resolutions agree with MC predictions
  including 5lt labs lt10cm.
• Further improvement expected with longer
  absorption length.

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Xenon Purification
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RGAwith a mass spectrometer

• Remaining Gas Analysis (RGA) for investigating
  what causes short absorption length in gamma beam
  test.
• Remaining gas in the chamber was sampled to the
  analyzing section.

• Vacuum level
• LP Chamber 2.0x10-2Pa
• Analyzing section 2.0x10-3Pa

He
H2O
N2
O2
Xe
Co2
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Purification 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 10-12cc/minute

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Performanceof the purification

• Modeling
• if no continuous outgassing

a event
Cosmic-ray event
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After 600 hours

• Light yield increased by factor of 4.
• Comparison with MC prediction ? labs gt 1m

After purification 83470 photoelectrons
Before purification 20590 photoelectrons
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Absorption Length Measurementsbefore
purificationafter purification
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Estimation ofAbsorption Length

• a cosmic-events.
• Relation between the light yield and distance
  from the light source to PMTs.

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Absorption Length (a)before purification

• Data/MC as a function of the distance from the
  alpha source to the PMTs
• MC lRay 30cm
• labs 8 cm and 7cm
• MC with 7cm absorption can explain rapid decrease
  of the light yield at short distance.

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Absorption Length (CR)before purification
100cm

• Data distribution is steeper near the face and
  falls less violently for large z.
• The discrepancy can be explained by introducing
  wavelength-dependent absorption effect by water.
• Absorption length 510cm

50cm
10cm
5cm
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Absorption Lengthafter purification

• Fit the data with a function A exp(-x/ labs)
• labs gt100cm (95 C.L) from comparison with MC.
• (labsgt80cm from comparison with cold gas data
  which however includes diffusion effect)
• CR data indicate that labs gt 100cm has been
  achieved after purification.

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Other related RDPMTPurity monitor
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PMT Development
Aluminum Strip

• The previous model used a Mn layer to keep the
  surface conductivity of the photocathode at low
  temperature.
• The new model uses Al strip instead of the Mn
  layer.
• QE is expected to improve and PMT production in
  more constant quality.

New Model
Previous Model
window
light
Mn layer
Photocathode
300um Al strip
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PMT test in gas/liquid xenon
New model

• Tests in cold gas and in liquid xenon performed.
• QE improved by factor of 2-3.
• Rate dependence is similar or slightly better.
  (need careful check)
• K-Cs-Sb photocathode can probably be used
  (Previous model with Rb-Cs-Sb) ? possible to
  achieve higher gain with same HV.

Previous model
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Purity Monitor

• By measuring concentration of electro-negative
  impurities
• By measuring absorption of scintillation light

• Laser-induced ionization chamber
• Laser stability can be monitored by measuring
  cathode signal.
• Large amount of light yield.
• Possible to measure impurity 1ppm1ppb.
• Need development, but we can use a similar one as
  ICARUS developed.

• a source ionization chamber
• Simple and stable.
• Possible to measure impurity of 10100ppb.
• Signal amplitude is rather small, a few mV level
  for 100ppb impurity.
• Implemented in LP.

Anode signal Q
Laser Nd-Yag (266nm) or xenon lamp
3mm
Am a source
Cathode signal Q0
Al photocathode

• Cosmic-ray event Possible to measure labs gt1m
  but low rate.
• a event Possible to measure labs 1m but
  small signal.
• Other possibilities Direct observation of laser
  light through xenon (Exima laser is a
  candidate, under investigation).

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Final Detectorcalibrationexpected
performancecryogenics design
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Calibration
Eg
q
170o
Eg

• p-p?p0n
• p0(28MeV/c) ? g g
• 54.9 MeV lt E(g) lt 82.9 MeV
• Am-Be g source 4.43 MeV

Eg
p0
175o

• Requiring qgt170o
• FWHM 1.3 MeV
• Requiring q gt 175o
• FWHM 0.3 MeV

g
p-
q
54.9MeV
82.9MeV
g

• No need of excellent energy resolution.
• Position resolution of s45cm is enough.
• Timing resolution (s lt 1nsec) is required for
  timing calibration of the xenon detector.

1.3MeV for qgt170o 0.3MeV for qgt175o
Eg
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Calibration contd
Crystal box PRD 38(1988)2077

• m?egnn
• Eegt0.85 Eggt0.8 qeg gt 120o

108m/sec
R.Tribbles talk at Univ. of Tokyo Oct. 1999
Accidental background
107m/sec Signal 1/10 Background lt1/100
Accidental background
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Cryostat design
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Schedule

• Jul/02 Jul/02
  Aug/02 Sep/02 Oct/02 Nov/02
  Dec/02 Jan/03 Feb/03 Mar/03
• -----------------------------------------------
  ----------------------------------------------
  --------------------------------------------
• Large Prototype RD
• Purification RD
• 1st Purification test --------gt
• Purity monitor
  lt------------------------------------gt- - - - -
  - - -
• 2nd purification test
  lt----------gt
• PMT RD ------------------------------
  -----------------gt
• 3rd g beam test
  lt-----------gt
• (Electron beam test)
  
  lt-----------gt
• Analysis
  
  lt------------------------gt
• Final detector construction
• Cryostat design ----------gt - - - - - -
• Honeycomb -
• RD, construction - - - - - -
  lt-------------------------------------------------
  -gt

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Summary

• 2nd g beam test in Feb. 02
• Worse resolutions than our expectation due to
  short absorption length caused by contaminant
  impurity.
• Purification system has been developed and 1st
  test was successfully done.
• Recent CR and alpha data indicate labsgt1m.
• Increasing purification speed is the next step
  for quick start of the detector operation.
• Development of purification monitor is an
  important issue.
• Another tests are planed with purified xenon
  using g and e beams in autumn.
• Other RD works are going.