R

1
RD works on Liquid Xenon Photon Detectorfor
µge? experiment at PSI

• Outline
• Introduction
• Prototype RD works
• Summary

• Satoshi Mihara
• ICEPP, Univ. of Tokyo

2
Introduction, µge? at PSI
aims to achieve the sensitivity down to
Br(µge?)10-14

• Detect e and ?, back to back and in time
• 100 duty factor continuous beam of 108µ/sec
• Liquid Xe photon detector
• Solenoidal magnetic spectrometer with a graded
  magnetic field

http//meg.psi.ch
STARTS IN 2003 and RUNS 1- 2 years
3
Introduction,contd

• µ beam stopped on the target 108/sec
• Ee52.8MeV E?52.8MeV
• Back to back, in time
• Sensitivity
• Nm1x108/sec, 2.2x107 sec running
  O/4p0.09,ee0.95, e?0.7, and esel0.8
• aSingle Event sensitivity 0.94x10-14
• Main background sources
• Radiative µ decay
• Accidental overlap
• NOT back to back, NOT in time
• Reduced down to 10-15 level

?
µ
e
µge???
µge???
?
?
?
?
?
e
?
e
?
4
Requirement on the Photon Detector

• Good Energy Resolution
• Good Position Resolution
• Good time Resolution

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Liquid Xe Photon Detector

• 800 liter liquid Xe
• 800 PMTs inside liquid(HAMAMATSU R6041Q)

• Detect scintillation light(?175nm) from Liq.
  Xe(-100?)
• Fast response, Good Energy, and Position
  resolutions
• Wph 24 eV
• (c.f. Wph(NaI) 17eV)
• tfast 45nsec
• Mini-Kamiokande type

NaI too slow CsI, BGO poor resolution
at 52.8MeV Inhomoginity to cover large
area
!
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Strategy for the Detector Construction

• PMT Development
• Refrigerator Development
• Purification System Development
• Attenuation Length Measurement

• Small Prototype
• Large Prototype
• Final Detector

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Small Prototype ofLiquid Xe Photon Detector

• 32 2-inch PMTs surround the active volume of 2.34
  liter
• ?-ray sources of Cr,Cs,Mn, and Y
• a source for PMT calibration

• Metal channel dynodes
• Possible to be operated at low -100o
• Silica window to transmit UV light
• Typical gain 106, Typical Q.E. 10
• Possible to sustain up to 3 atom

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Small PrototypeExperimental Procedure

• Xenon liquified with a nitrogen cooling pipe
• Kept in stable temp.(-100o) and pressure (1.2
  atom) by controlling the flow of liquid nitrogen
• PMT operation in liquid xenon has been successful
  for more than one month

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Small PrototypeSignal from PMTs

• Typical PMT output for liq. Xe scintillation
  light
• Triggering condition for ? ray events
• (ex. For g from Mn)
• gt 220 p.e. in R1
• gt 50 p.e. in R2
• gt 10 p.e. in R3
• gt 100 p.e. in E1
• gt 20 p.e. in E2
• Loose enough to trigger
• Almost all events where ?
• interacted well inside the
• sensitive volume

c
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Small PrototypeAnalysis

• Position of ? interaction
• Weighting the position of the PMTs with their
  individual pulse heights
• For selecting the fully contained events
• Requiring the ? int. position should lie within
  a central region of 2cmx1cmf

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Small PrototypeResult, Energy Resolution

• Fitting the spectrums with an asymmetric Gaussian
  function.
• Results are compared with MC prediction.
• Simulation of ? int. and energy deposition EGS4
• Simulation of the propagation of scint. Light
• EGS cut off energy 1keV
• Att. Length (absorption)29cm
• Wph 24eV
• 0.7 in s is expected at 52.8MeV.

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Small PrototypeResult, Position Resolution

• PMTs are divided into two groups by the y-z
  plane.
• ? int. positions are
• calculated in each
• group and then
• compared with
• each other.
• Position resolution
• is estimated as
• sz1-z2/v2
• Possible to achieve for 52.8MeV ?
• slt3mm in position meas.

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Small PrototypeResult, Time Resolution

• PMTs are divided again into two groups by the y-z
  plane.
• In each group the average of the time measured by
  TDC is calculated after slewing correction for
  each PMT.
• The time resolution
• is estimated by
• taking the difference
• between two groups.
• Resolution improves
• as 1/vNpe
• slt50psec
• at 52.8 MeV.

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Short Summary on the Small Prototype
Extrapolation to Higher Energy

• Energy 0.7
• Position lt3mm
• Time lt50psec

in s at 52.8MeV
Excellent!
Go to the next step Large Prototype
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Large PrototypeHow Large?

• To study the detector response to higher energy ?
  rays, large volume is required to fully contain
  events.

Depth
40cm x 40cm x 50cm Active Volume
224 PMTs
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Large PrototypeVessel Design

• Vessel should be large enough to install the
  detector.
• Possibility to reuse for future PMT calibration.
• Thinner entrance window thickness.
• Thermal insulation.
• Most of all components used in the final detector
  should be tested in Large Prototype.
• Refrigerator
• Feedthrough
• PMT holder structure
• Surface level meter etc, etc

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Construction ofthe Large Prototype Vessel
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Construction of the Large Prototype Vessel

• Pressure test up to 0.6MPa
• Vacuum leak test
• Cooling test with liquid nitrogen

All OK. Ready to fill liquid xenon inside
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Assembling

• Holder
• Front G10, Plastic
• Side, RearAluminum
• Blue LEDs for PMT gain adjustment
• a sources for calibration
• Temperature sensors
• Surface Level meter

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Pulse Tube Refrigerator

• Conventionally liq. Nitrogen has been used
• g waste of nitrogen, not suitable for long
  term physics experiment.
• Purse tube refrigerator is the best for this
  purpose since there is no moving part
• in the low temperature stage.

Pressure Oscillation
Mechanically moving
70W
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Liquefaction Test

• Pre-cooling before liquefaction
• with 0.2MPa gas xenon inside.
• Liquefaction of xenon 100 liter liquid for 2
  day (2.0 liter/hour) .
• Recondensation using the refrigerator was
  successfully done.
• Several basic measurements done.

• PMTs operated for 2.5 days stably.
• Calibration with LED and a source signals done
• Currently preparing ? beam test in June.

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? beam at TERAS

• Use inverse-compton scattered ? beam provided at
  TERAS in ETL AIST in Tsukuba, Japan.
• E?10,20,30,40MeV
• ? beam intensity 1kHz (typ.)
• Analyze the edge of the Compton photon spectrum.
• Test will start in the middle of June.

40MeV ?
NaI
Taken after acc. trouble. Better BG condition now!
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Plan for Attenuation Length Measurement

• Step1
• PMT1Absorption Scattering Length meas.
• PMT2 used as a reference.
• Collimators to prevent scinti. light from hitting
  the wall.
• Mask in fron of PMT1 to define the illuminated
  are on the photo cathode.

Liq. Nitrogen
PMT1
Step2 PMT2 Scatt. Length meas. PMT1 reference
at a fixed point.
PMT2
dL/L 5 x L(m)
X ray
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Summary

• Small Prototype
• Small prototype of liquid Xe photon detector was
  successfully constructed and tested with ?-ray
  sources of 320keV-1836keV.
• Scintillation light from xenon is directly
  observed with PMTs located inside the liquid.
• Excellent Energy, Position, Time resolutions.
• Large Prototype
• 100 liter liquefaction test was successfully
  done.
• Currently preparing for a large prototype test
  using inverse-compton scattered beam of higher
  energy ? rays gt 40MeV.

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Summary contd

• Refrigerator
• Recondensation of 100 liter of liq. Xenon was
  successful.
• Studying other coolants for obtaining better
  cooling efficiency.
• Attenuation Length Measurement
• Setup construction is going on.
• Measurements will start in this autumn at
  Novosibirsk.
• Final Detector
• Design work just started.
• Xenon, ? window, PMT mass-production.