2000 Fiscal Year Final Research Report Summary
Research for neutrino masses using solar neutrinos
| Project/Area Number |
10440071
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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 | University of Tokyo |
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Principal Investigator |
NAKAHATA Masayuki ICRR, Univ.of Tokyo, Assistant Professor, 宇宙線研究所, 助教授 (70192672)
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| Co-Investigator(Kenkyū-buntansha) |
INOUE Kunio Physics department, Tohoku Univ. Assistant Prof., 理学部, 助教授 (10242166)
FUKUDA Yoshiyuki ICRR, Univ.of Tokyo, Research assistant, 宇宙線研究所, 助手 (40272520)
SUZUKI Yoichiro ICRR, Univ.of Tokyo, Professor, 宇宙線研究所, 教授 (70144425)
MIURA Makoto ICRR, Univ.of Tokyo, Research assistant, 宇宙線研究所, 助手 (10272519)
TAKEUCHI Yasuo ICRR, Univ.of Tokyo, Research assistant, 宇宙線研究所, 助手 (60272522)
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| Project Period (FY) |
1998 – 2000
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| Keywords | Neutrino / Solar neutrino / Super-Kamiokande / Neutrino oscillation |
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| Research Abstract |
Research for neutrino masses has been performed using the 1258 days' solar neutrino data taken by Super-Kamiokande. Super-Kamiokande is able to measure day/night variation of solar neutrino flux and energy spectrum of solar neutrinos with unprecedented high accuracy. They are purely due to property of neutrinos as an elementary particle and it does not depend upon the details of solar models. So, if anomaly in those measurements are found, it should be a direct evidence of neutrino masses. To the contrary, if anomaly is not observed, it should strongly constrain neutrino oscillation parameters (neutrino mass difference and mixing angle). By improving the analysis method by this research, we are able to analyze data down to 5 MeV.For the day/night analysis, the obtained day/night asymmetry of the solar neutrino flux was 3.3%±2.2% (stat.)+1.3/-1.2% (sys.). Although it is 1.3 sigma away from zero, it is not statistically significant. For the analysis of the spectrum shape of solar neutrinos, observed shape of the energy spectrum is consistent with the expected spectrum shape with 39% confidence level (CL). From those measurements, strong constraint on the neutrino oscillation parameters are obtained and small mixing angle solution of the solar neutrino problem is disfavored with about 95% CL.The observed flux of solar neutrinos is only 45% of the expected flux from the standard solar models. Taking into account the deficit of the observed absolute flux, large mixing solutions are favored in the solar neutrino oscaillations.
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