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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.)

Research Project

Project/Area Number 03101002
Research Category

Grant-in-Aid for Specially Promoted Research

Allocation TypeSingle-year Grants
Research InstitutionThe University of Tokyo

Principal Investigator

TOTSUKA Yoji  Institute for Cosmic Ray Research, The university of Tokyo, Professor, 宇宙線研究所, 教授 (40011712)

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)
Project Period (FY) 1991 – 1994
KeywordsAtomspheric neutrinos / Neutrino oscillations / Muon-neutrino / Eletron-neutrino / Tau-neutrino / Neutrino mass
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.

  • Research Products

    (14 results)

All Other

All Publications (14 results)

  • [Publications] K.S.Hirata,et al.: "Observation of a small atmospheric νμ/νe ratio in kamiokande" Physics Letters B. 280. 146-152 (1992)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] E.W.Beier,et al: "Survey of atmospheric neutrino data and implications for neutrino mass and mixing" Physics Letters B. 283. 446-453 (1992)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] Y.Totsuka: "Solar and Atmospheric Neutrinos Observed at Kamiokande" Nuclear Physics B. 28A. 67-74 (1992)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] Y.Totsuka: "Atmospheric Neutrinos--Updated Results--" Nuclear Physics B. 31. 428-437 (1993)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] Y.Fukuda et al: "Atmospheric νμ/νe ratio in the multi-GeV energe range" Physics Letters B. 335. 237-245 (1994)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] 戸塚洋二: "素粒子物理" 岩波書店, 218 (1992)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] A.Suzuki et al: "Physics and Astrophysics of Neutrinos" Springer-Verlag, 934 (1994)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] K.S.Hirata, et al.: "Observation of a Small Atmospheric nu_<mu>/nue Ratio in Kamiokande" Physics Letters B. 280. 146-152 (1992)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] E.W.Beier, et al.: "Survey of atmospheric neutrino data and impkications for neutrino mass and mixing" Physics Letters B. 283. 446-453 (1992)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] Y.Totsuka: "Solar and Atomspheric Neutrinos observed at Kamiokande" Nuclear Physics B. 28A. 67-74 (1992)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] Y.Totsuka: "Atmospheric Neutrinos-Updated Results-" Nuclear Phsics B. 31. 428-437 (1993)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] Y.Fukuda, et al.: "Atmospheric nu_<mu>/nue Ratio in the Multi-GeV Energy Range" Physics Letters B. 335. 237-245 (1994)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] Y.Totsuka: High-Energy Physics. Iwanami, 218 (1992)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] A Suzuki and M.Fukugita: Physics and Astrophysics of Neutrinos. Springer-Verlag, 934 (1994)

    • Description
      「研究成果報告書概要(欧文)」より

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Published: 1996-04-15  

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