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PMT absolute calibration using the Rayleigh scattering in Nitrogen air PMT absolute calibration using the Rayleigh scattering in Nitrogen air S. Yoshida, Chiba University

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Motivation Absolute calibration ： Laser energy can be measured by energy meter preciously. Rayleigh scattering is well understood. Scattered Laser beam provides a well-calibrated Single p.e. source!

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Proof of the Concept Proof of the Concept Absolute calibration using N 2 laser (CRAY)

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System overview

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Components Light source (Laser Science VSL-337ND-S) N 2 laser lambda ＝ 337.1nm E max =300uJ Pulse width<4nsec Si energy probe (Laser Probe RjP-465) 500fJ-250nJ Detection area:1.0cm 2 Accuracy=+-5%

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PMT(H7195PX) Size of photo cathode ＝ 60mm phi HPK provides their calibration data. (Only 25 ｍｍ phi @center) （ Both of the errors of HPK Q.E. and C.E. are 10%.) Q.E.C.E. Ch125.96%74% Ch225.78%77%

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Scattering region Pure N 2 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 N 2 flow start, calibration is started.

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Rayleigh scattering ｎ ： refractive index(1.0002936 for stp N 2 ) λ ： wavelength (337.1nm) F k ： Correction factor for anisotropy of non-spherical molecules(1.03679 for N 2 ) For stp N2, （ H.Naus and W.Ubachs, Opt lett, 25 5 347 2000 ）

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Calculation of # of photon in PMT N pulse : # of photon in each laser pulse –When 1.0uJ, 1.697x10 12 photon N mol : # 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 glasslaser Pyro (Accuracy = +-5% ) Si (Accuracy = +-5% )

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Calculation of # of photo-electron N 0 : # of events below threshold N : # of events above threshold μ: average of # of P.E. Peak Threshold=(1/3)xPeak ADC distribution

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Absolute calibration of PMT1 # of photon from Si det. N photon =0.50±0.03 # of P.E. from PMT. N pe =0.093±0.01 Q.E.×C.E=0.18±0.02 (Data provided by HPK ： Q.E.×C.E.=0.19±0.03) Our Concept works out!!

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New CRAY Chamber Monitoring N2 Scattering by The calibrated tubes Aperture Limiter The IceCube PMT

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Photon beam with 50 mm diameter scans the cathode Beam PMT Box Chamber Calibration PMTs N 2 laser Rotation Bed Attachment for the IceCube PMT

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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. N photon =0.50 ±0.03 # of P.E. from PMT. N pe =0.11±0.01 Q.E.×C.E=0.21±0.02 (Data provided by HPK: Q.E.×C.E.=0.21±0.03)

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Error estimation (very preliminary) Calibration of energy meter ： ±5% 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.

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