1994 Fiscal Year Final Research Report Summary
Study of the nu_<mu>-deficit in the atmospheric neutriono fluxes. (Study of the origin of neutrino mass.)
| Project/Area Number |
03101002
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| Research Category |
Grant-in-Aid for Specially Promoted Research
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| Allocation Type | Single-year Grants |
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| Research Institution | The University of Tokyo |
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Principal Investigator |
TOTSUKA Yoji Institute for Cosmic Ray Research, The university of Tokyo, Professor, 宇宙線研究所, 教授 (40011712)
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| Co-Investigator(Kenkyū-buntansha) |
NAKAHATA Masayuki Institute for Cosmic Ray Research, The University of Tokyo, Asistant, 宇宙線研究所, 助手 (70192672)
SUZUKI Atsuto Faculty of Science, Tohoku University, Professor, 理学部, 教授 (00100818)
MIYANO Kazumasa Faculty of Science, Niigata University, Professor, 理学部, 教授 (10011529)
NISHIKAWA Koichiro Institute for Nucler Study, The University of Tokyo, Asociate Professor, 原子核研究所, 助教授 (60198439)
KAJITA Takaaki Institute for Cosmic Ray Research, The university of Tokyo, Asociate Professor, 宇宙線研究所, 助教授 (40185773)
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| Project Period (FY) |
1991 – 1994
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| Keywords | Atomspheric neutrinos / Neutrino oscillations / Muon-neutrino / Eletron-neutrino / Tau-neutrino / Neutrino mass |
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| Research Abstract |
In 1994, a beam experiment was carried out to study the efficiency of separating electrons and muons, and to study various detector effects related to the nu_<mu>-deficit in the atmospheric neutrino fluxes. The result from this experiment showed that the efficiency of separating electrons and muons was 98% as expected by our Monte Carlo simulation. This result suggests that the atmospheric nu_<mu>-deficit is probably related to a real physics such as neutrino oscillations.
The total number of atmospheric neutrino events was nearly doubled during this research period. The observed (nu_<mu>/nu_e) ratio relative to the expected one, (nu_<mu>/nu_e) _<Data>/ (nu_<mu>/nu_e) _<MC>, was 0.60<plus-minus>0.055 (stat.)<plus-minus>0.05 (syst.) at the sub-Gev energy range. The statistical significance of the nu_<mu>-deficit was about 5sigma.
We also studied the atmospheric neutrino fluxes in the multi-GeV energy range. We observed nu_<mu>-deficit in this energy range too. The observed zenith-angle dependence of the nu_<mu>/nu_e ratio in this energy range was not uniform and was consistent with the expectation from neutrino oscillations.
From those studies, we concluded that neutrino oscillations might account for the atmospheric netrino data. The mass of either nu_<mu>mu or nutau might be about 0.1 eV.
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