PMT absolute calibration using the Rayleigh scattering in

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

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!

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

System overview

Components • Light source (Laser Science VSL-337 ND-S) N 2 laser lambda＝ 337. 1 nm Emax=300 u. J Pulse width<4 nsec • Si energy probe (Laser Probe Rj. P-465) 500 f. J-250 n. J Detection area: 1. 0 cm 2 Accuracy=+-5%

• PMT(H 7195 PX) Size of photo cathode＝ 60 mm phi HPK provides their calibration data. (Only 25ｍｍ phi @center) （Both of the errors of HPK Q. E. and C. E. are 10%. ) Q. E. Ch 1 25. 96% 74% Ch 2 25. 78% 77%

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.

Rayleigh scattering ｎ ：refractive index(1. 0002936 for stp N 2) λ ： wavelength (337. 1 nm) Fk ： Correction factor for anisotropy of non-spherical molecules(1. 03679 for N 2) （H. Naus and W. Ubachs, Opt lett, 25 5 347 2000） • For stp N 2,

Calculation of # of photon in PMT • Npulse: # of photon in each laser pulse – When 1. 0 u. J, 1. 697 x 1012 photon • Nmol : # density of molecule • A : Acceptance of PMT (include dir. dependence) • l: Length of scattering region

Polarization of laser beam The angle of polarizer is changed and then laser energy is measured. Within +-5%

Laser energy cross check laser glass Si (Accuracy = +-5% ) Pyro (Accuracy = +-5% )

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

Absolute calibration of PMT 1 # of photon from Si det. Nphoton=0. 50± 0. 03 # of P. E. from PMT. Npe=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!!

New CRAY Chamber Monitoring N 2 Scattering by The calibrated tubes Aperture Limiter The Ice. Cube PMT

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

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

Things to Consider • The photon wavelength from N 2 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 $$.

Backup slides

Absolute calibration of PMT 2 # of photon from Si det. Nphoton=0. 50 ± 0. 03 # of P. E. from PMT. Npe=0. 11± 0. 01 Q. E. ×C. E=0. 21± 0. 02 (Data provided by HPK: Q. E. ×C. E. =0. 21± 0. 03)

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.