PMT absolute calibration using the Rayleigh scattering in Nitrogen air

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PMT absolute calibration using the Rayleigh
scattering in Nitrogen air

• S. Yoshida, Chiba University

2
Motivation

• Absolute calibration
• Laser energy can be measured by energy meter
  preciously.
• Rayleigh scattering is well understood.

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Proof of the Concept
Absolute calibration using N2 laser (CRAY)
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System overview
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Components

• Light source
• (Laser Science VSL-337ND-S)
• N2 laser
• lambda337.1nm
• Emax300uJ
• Pulse widthlt4nsec
• Si energy probe
• (Laser Probe RjP-465)
• 500fJ-250nJ
• Detection area1.0cm2
• Accuracy-5

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• PMT(H7195PX)
• Size of photo cathode60mm phi
• HPK provides their calibration data.
• (Only 25mm phi _at_center)
• (Both of the errors of HPK Q.E. and C.E. are
  10.)

Q.E. C.E.
Ch1 25.96 74
Ch2 25.78 77
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Scattering region

• Pure N2 gas (99.9995) is introduced.
• Flow rate is 5 10 litter/minutes
• Temperature and pressure is monitored
• by environmental data logger.
• 1 hour after of N2 flow start, calibration is
• started.

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Rayleigh scattering
n refractive index(1.0002936 for stp N2) ?
wavelength (337.1nm) Fk Correction factor for
anisotropy of non-spherical
molecules(1.03679 for N2)
(H.Naus and W.Ubachs, Opt lett, 25 5 347 2000)

• For stp N2,

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Calculation of of photon in PMT

• Npulse of photon in each laser pulse
• When 1.0uJ, 1.697x1012photon
• Nmol density of molecule
• A Acceptance of PMT (include dir. dependence)
• l Length of scattering region

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Polarization of laser beam
The angle of polarizer is changed and then laser
energy is measured.
Within -5
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Laser energy cross check
Pyro (Accuracy -5 )
glass
laser
Si (Accuracy -5 )
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Calculation of of photo-electron

• N0 of events below threshold
• N of events above threshold
• µ average of of P.E.

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Absolute calibration of PMT1

• of photon from Si det.
• Nphoton0.500.03
• of P.E. from PMT.
• Npe0.0930.01

Q.E.C.E0.180.02
(Data provided by HPK Q.E.C.E.0.190.03)
Our Concept works out!!
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New CRAY Chamber
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Attachment for the IceCube PMT

• Photon beam with 50 mm diameter scans the cathode

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Summary

• PMT absolute calibration method using Rayleigh
  scattering by pure gas has been developed.
• The measured Q.E.xC.E. is consistent with HPK
  result.
• A new chamber is now being designed and built.
• Absolute calibration of the IceCube PMT is
  scheduled to start in this coming February.
• Watch out our report in the next collaboration
  meeting.

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Things to Consider

• The photon wavelength from N2 laser is 337 nm,
  which may be too short for the DOM pressure
  glass.
• On the other hand, we can MEASURE the DOM sphere
  absorption coefficient at 337 nm.
• The wavelength changeable laser is available but
  needs more .

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Backup slides
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Absolute calibration of PMT2

• of photon from Si det.
• Nphoton0.50 0.03
• of P.E. from PMT.
• Npe0.110.01

Q.E.C.E0.210.02
(Data provided by HPK Q.E.C.E.0.210.03)
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Error estimation (very preliminary)

• Calibration of energy meter5
• Polarization of beam 0.5
• Acceptance calculation 2
• Scattering calculation 3
• Reflection inside of box 2?
• Geomagnetic field 5?
• Reproducibility of 1 p.e. 10

of Photon
of P.E.