Requirement for photon-detectors at directional measurement of anti-neutorinos with KamLAND Mio Nakamura Research Center for Neutrino Science,Tohoku University KamLAND KamLAND ・・・ 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 ) PMTs( Φ17or20 inch ) are set around the balloon detect scintillation to decide vertex from time difference of signal. Test of SCITIC with LS SCITIC ・・・ 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. How to detect? ②② ① ① 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. The problem ① directional data is lost for the neutron’s thermal diffusion and  -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  -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 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. KamLAND LS B loaded LS (1.0%) Li loaded LS (0.15%) Li loaded LS (1.5%) 20 MeV 10 MeV 5 MeV 3 MeV 2 MeV We want to know which direction anti-neutrinos come 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. Neutron angle depends on incoming neutrino direction in low energy. ◆ Feature of I.I. ( courtesy of KEK ) Active area : φ100mm Gain : ~10 6 Q.E. : 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 214 Bi 214 Po 222 Rn 210 Pb β-decay prompt signal α-decay delayed signal 164μs KamLAND LS + BisMSB We want directional sensitive photo detectors with gain instead of PMT. Position resolution etc. is good compared to PMT. But ⑴ Active area of MPPC is too small ・・・ →Can active area of MPPC be larger? ⑵ MPPC 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. ⑶ The 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”! Feature of PSD is that it is connected to 4 readout channels to 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 amplifier because 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. θ n <35 ° Excellent! ◆ MPPC ◆ CCD+I.I. CCD camera