PMT absolute calibration PMT absolute calibration using the Rayleigh scattering using the Rayleigh scattering

in Nitrogen airin Nitrogen air 　　S. Yoshida, Chiba UniversityS. Yoshida, Chiba University

MotivationMotivation

• 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 ConceptProof of the ConceptAbsolute calibration using N2 laser (CRAY)

System overviewSystem overview

ComponentsComponents

• Light source(Laser Science VSL-337ND-S)

N2 laser lambda ＝ 337.1nmEmax=300uJPulse width<4nsec

• Si energy probe(Laser Probe RjP-465)

500fJ-250nJDetection area:1.0cm2

Accuracy=+-5%

• PMT(H7195PX)Size of photo cathode ＝ 60mm phiHPK 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.

Ch1 25.96% 74%

Ch2 25.78% 77%

Scattering regionScattering 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.

Rayleigh scatteringRayleigh scattering

)cos1(16

3

)2(

)1(24 22224

223

kFnN

n

d

d

ｎ ： refractive index(1.0002936 for stp N2)λ ： wavelength (337.1nm)Fk ： Correction factor for anisotropy of non-spherical molecules(1.03679 for N2)

• For stp N2,

（ H.Naus and W.Ubachs, Opt lett, 25 5 347 2000 ）

)(cm108179.3 226 total

Calculation of # of photon in PMTCalculation 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

AlNNN moltotalpulsephoton

Polarization of laser beamPolarization of laser beam

The angle of polarizer is changed and then laser energy is measured.

Within +-5%

Laser energy cross checkLaser energy cross checkglasslaser Pyro (Accuracy = +-5% )

Si (Accuracy = +-5% )%.ΔE

REE

EE

Si

FresnelPyroSi

SiPyro

76

)nJ(525.6)calc(

)nJ(959.6),μJ(7.234

Calculation of # of photo-electron Calculation of # of photo-electron

• N0 : # of events below

threshold

• N : # of events above threshold

• μ: average of # of P.E.

Peak

Threshold=(1/3)xPeak

ADC distribution

n

i

i

all

all

iNN

NN

1

0

!

exp

exp

Absolute calibration of PMT1Absolute calibration of PMT1

# 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 ChamberNew CRAY ChamberMonitoring N2

Scattering by

The calibrated tubes

Aperture Limiter

The IceCube PMT

•Photon beam with 50 mm diameter scans the cathode

Beam

PMT Box

Chamber

Calibration PMTs

N2 laser

Rotation Bed

Attachment for the IceCube PMAttachment for the IceCube PMTT

SummarySummary

• 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 sche

duled to start in this coming February.• Watch out our report in the next collaboration me

eting.

Things to ConsiderThings 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 $$.

Backup slidesBackup slides

Absolute calibration of PMT2Absolute calibration of PMT2

# 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)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.