1993 Fiscal Year Final Research Report Summary
Detection of High Energy Neutrino and Gamma Ray
| Project/Area Number |
04452021
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
核・宇宙線・素粒子
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| Research Institution | Institute for Nuclear Study, Univ.of Tokyo |
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Principal Investigator |
NISHIKAWA Kouitirou INS.University of Tokyo, Associate Professor, 原子核研究所, 助教授 (60198439)
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| Co-Investigator(Kenkyū-buntansha) |
SASAKI O. National Lab.for High Energy Phys., Research Associate, 助手 (30178636)
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| Project Period (FY) |
1992 – 1993
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| Keywords | Astrophysical Neutrino |
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| Research Abstract |
Feasibility of a large water Cherenkov detector on the surface for high energy neutrinos of astrophysical origin was examined, using a 1000m^2 prototype detector. The data was taken in early part of 1992.
(1) Trigger rate :
The signal for high energy neutrino is upward-going muon, which is created by the charged current interaction of neutrino with rock under the detector. This flux is estimated to be an order of 10^<-10> of that of cosmic rays. This huge background has been suppressed by utilizing the directionality of the Cherenkov light.20" phototube has been placed 10m below the water surface, with 5m separation. The trigger requires more than 4 phototube has been hit with 30ns coincidence time window. Even with this simple trigger can attain a background suppression of the order of 10^5, giving about 4Hz trigger rate.
(2) The composition of the events :
The composition of the events has been analyzed, using the pulse height in the upper part of the detector which is optically separated from the main part of the detector. The analysis showed about half of the triggering events are due to air shower which deposit large pulse height in the upper part of the detector. The rest of the events are due to muons which have large zenith angle.
(3) The final background rejection capability :
The 20" phototube has been calibrated, using cosmic ray muons by the additional phototube which has been purchased in 1992-1993. An analysis, using both timing and pulse height information, yields about 2x10^<10> suppression of the backgrounds.
We believe that the original motivation of this study, i.e.feasibility of operation of a large water Cherenkov detector on the surface, has been proved.
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