1999 Fiscal Year Final Research Report Summary
Determination of the Atmospheric Neutrino Flux by the Observation of Atmospheric Gamma
| Project/Area Number |
09440110
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
素粒子・核・宇宙線
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| Research Institution | Shibaura Institute of Technology |
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Principal Investigator |
KASAHARA Katsuaki Systems Engineering, Shibaura Institute of Technology, Professor, システム工学部, 教授 (00013425)
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| Co-Investigator(Kenkyū-buntansha) |
YOSHIDA Kenji Engineering, Kanagawa Univ., Assistant, 工学部, 助手 (90260984)
TAMARU Tadahisa Engineering, Kanagawa Univ., Assistant, 工学部, 助手 (90271361)
TORII Shoji Engineering, Kanagawa Univ., Associate Professor, 工学部, 助教授 (90167536)
TANAKA Naohiko Systems Engineering, Shibaura Institute of Technology, Lecturer, システム工学部, 専任講師 (10255648)
WATANABE Eiji Systems Engineering, Shibaura Institute of Technology, Associate Professor, システム工学部, 助教授 (40191746)
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| Project Period (FY) |
1997 – 1999
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| Keywords | Atmospheric Neutrinos / Neutrino Oscillation / Scintillating Fiber / Atmospheric Gamma Rays / Cosmic Rats / Kamioka Experiment / Atmospheric Muons / MuonNeutrino Deficit |
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| Research Abstract |
First year: We have upgraded the trigger system of the BETS originally designed for the observation of primary cosmic electrons; a multi trigger system was realized by which we can observe gamma rays with different trigger conditions simultaneously.
Second year: We selected Mt. Norikura Observatory of Tokyo University (〜2800 m) as a site where we could do an observation meaningful for the calibration of atmospheric neutrino calculations as well as the test of the detector, We made 3 week observation. The trigger rate was coincident with the calculation within 2〜3%. However, the vertical flux of the gamma rays was deviated from the calculation. This contradiction was now well resolved by improving the data analysis method.
Third year: 1) The observation is at the balloon altitudes so that a number of charged particles are expected to enter from the side of the detector. To reject such particles, we added 4 plastic scintillator plates of size 30cmx 5cmx 1.5cm around the top part of the det
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ector, For read-out, we embedded 8 thin fibers in each plate and they are read by a small PMT. 2) The balloon was launched at Sanriku Balloon Center on Sep., 2, 1999 and recovered after 〜10 hour flight. The trigger rates from the sea level to 25 km were nicely coincident with a calculation and thus proved that both of the calculation and detector were well operating. We realized quasi level flight(〜30 min) at 15.3, 18.5, 21.2, and 24.7km above sea level, 3) The energy spectrum was obtained at these altitudes, and they are converted into the vertical flux. The spectrum was well approximated by a power at 3 to 30 GeV. The vertical fluxes at 15 to 21 km were well reproduced by the calculations using the BESS measured primary intensity. However, the observation gave a larger flux than the calculation above 25 km, This seems to be due to the lack of anti-coincidence scintillator at some part of the detector; at higher altitudes, more primary protons are expected and they can enter the detector as if neutral particles from the gap where there is no scintillator. These protons could be rejected by employing image analysis and preliminary result showed we could to it. In year 2000, we are adding anti-coincidence scintillator and making a balloon observation again. Using these results and the muons spectrum at various altitudes, we expect we can reduce a reliable neutrino flux. Less
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