Requirement for photon-detectors at directionalRequirement for photon-detectors at directionalmeasurement of anti-neutorinos with KamLANDmeasurement of anti-neutorinos with KamLANDRequirement for photon-detectors at directionalRequirement for photon-detectors at directionalmeasurement of anti-neutorinos with KamLANDmeasurement of anti-neutorinos with KamLAND

Mio Nakamura Research Center for Neutrino Science ,Tohoku University

KamLANDKamLAND ・・・ Kamioka Liquid Scintillator Anti-Neutrino Detector

　 Vertex reconstruction using time of flight with PMT

⇩ Imaging ( lens + photo detector )

　 Vertex reconstruction using time of flight with PMT

⇩ Imaging ( lens + photo detector )

KamLAND, constructed at 1000m underground from top of the mountain,has a balloon with a 6.5m radius, filled with 1 kton of Liquid Scintillator ( LS ). 1879 PMTs( Φ17or20 inch ) are set around the balloon detect scintillation to decide vertex from time difference of signal.

Test of SCITIC with LSTest of SCITIC with LSTest of SCITIC with LSTest of SCITIC with LSSCITIC ・・・ SCIntillation Tracking Image Camera

KamLAND’s targets :

Procedure ① Plastic Scintillators ( PS ) detect μ going through LS. ② PMT detect it, and open CCD’s gate. ③ CCD records the afterglow at fluorescence plane of

image intensifier ( I.I. ). ④ CCD send the image to PC.

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reactor ν e, geo ν e, solar ν e

How to detect?

②②

①①

This CCD will be adapted for recording 2-images at dozens μs intervals by HPK. ( Figure8 )

Why?→Li has large neutron-capture cross section, besides generates not γ-ray but α-ray. 　 α-ray doesn’t diffuse but stops at once. ( Figure3 ) So we can get directional data. ( Figure4 )　 And we can use also coincidence, because Li-loaded LS generates prompt and 　 delayed signal.

PMTs detect anti-neutorinos via the inverse β-decay reaction in LS. ( Figure1 )PMTs distinguish some signals of anti-neutrino from backgrounds with Coincidence.

Li-loaded LS is proper.Li-loaded LS is proper.

The problem 　 ① directional data is lost for the neutron’s thermal diffusion 　 and γ-ray diffusion( ~40cm ) 　 ② the position resolution of PMTs is not too high ( ~10cm at object )

The problem 　 ① directional data is lost for the neutron’s thermal diffusion 　 and γ-ray diffusion( ~40cm ) 　 ② the position resolution of PMTs is not too high ( ~10cm at object )

Requirement for photo detector ・ 1photo counting ・ Sequent data acquisition at 1μs or shorter interval ・ small data size at one acquisition　 ・ Position resolution at object 1cm or better ・ good time resolution ・ High gain

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1000m

Now we are researching and testing organic solvent for Li. （ example : EDTA, crown ether）

CCD imaged μ-track ! ( Figure6 )

Next, we want to observe 2-signals from Bi-Po ( Figure7 ) like anti-neutrino signal.

Now, CCD is adapted!

First aim : imaging cosmic-ray μ with 1L LS and CCD+I.I.

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Figure6 :μ track

KamLAND LSB loaded LS (1.0%)Li loaded LS (0.15%)Li loaded LS (1.5%)

20 MeV10 MeV 5 MeV 3 MeV 2 MeV

We want to know which direction anti-neutrinoscome from better than now.

If we can get directional data of reactor-neutrino,→it will be neutrino-oscillation with individual baseline.If we can get directional data of geo-neutrino,→we will observe directly the interior of the earth.

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Figure2 : energy dependence

Neutron angle depends on incoming neutrino direction in low energy.

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Figure4 : n event reconstructed po int

◆Feature of I.I. ( courtesy of KEK ) Active area : φ100mm Gain : ~106

Q.E. : 12% @ 422 nm Afterglow : a few μs ( a few ns pulse incidence )

◆Feature of CCD number of pixels : 3×10*5 type : interline readout rate : 82 frames/s

214Bi214Bi

214Po214Po

222Rn

210Pb

β-decayprompt signal

α-decaydelayed signal

164μs

KamLAND LS + BisMSB

We want directional sensitive photo detectors with gain instead of PMT.

Position resolution etc. is good compared to PMT.

But⑴Active area of MPPC is too small ・・・ →Can active area of MPPC be larger?

⑵MPPC generates several hundred kHz dark noise at room temperature. 　 →I think dark noise will be reduced by 1/1000 at 200K. So I will test it soon.

⑶The output pulses from the APD pixels pile up with each other, because all APD pixels are connected to 1 readout channel. →Pixel-size resolution is lost simply because of 1 readout.

Scintillation→8300photons/MeV

prompt-delayed→at 200μs interval

prompt-delayed→at 5μs interval

◆PSD

　→ Go to “Test of SCITIC with LS”!

effectiveactive areagain

1 photoncountingHV

quantumefficiency

positioinresolution

time resolutionÅiFWHMÅj

PMT É”430mm5Å~10*6 2000V22% Å`20cm3.5nsMPPC 1mmÅ~1mm2.4Å~10*6ok 100V 70% 1000É m0.25ns

Feature of PSD is that it is connected to 4 readout channelsto detect the center of gravity of multiple hits.（ It means directional data isn’t lost. ）So data size is small.And PSD must be combined with some amplifierbecause PSD has no gain.

◆PSD+MPPC

If MPPC has 4 readout channel, MPPC will be the detector getting the center of gravity of multiple hits and with gain !?I will investigate possibility using PSD+MPPC in KamLAND.

θn<35°

Excellent!

◆MPPC

◆CCD+I.I.

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Figure7 :Bi − Po reaction

effectiveactive area

quantumefficiency

positioinresolution

PSD12mmÅ~12mmÅ`50% 1.5É m

CCD camera