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1990 Fiscal Year Final Research Report Summary

Double Beta Decay and Neutrino

Research Project

Project/Area Number 61065005
Research Category

Grant-in-Aid for Specially Promoted Research

Allocation TypeSingle-year Grants
Research InstitutionOsaka University

Principal Investigator

EJIRI Hiroyasu  Osaka Univ. Professor, 理学部, 教授 (80013374)

Co-Investigator(Kenkyū-buntansha) SHIBATA Tokushi  Tokyo Univ. INS Professor, 原子核研究所, 教授 (80028224)
WATANABE Takayuki  Tokyo Univ. Research Associate, 理学部, 助手 (80202414)
OHSUMI Hideaki  Osaka Univ. Research Associate, 理学部, 助手 (70176882)
SANO Hirokazu  Osaka Univ. Research Associate, 理学部, 助手 (00205999)
OKADA Kenji  Kyoto Industrial Univ. Assistant Professor, 計算機科学研究所, 助教授 (90093385)
Project Period (FY) 1986 – 1990
KeywordsNucleus / Elementary Particle / Neutrino / Double Beta Decay / Ground Unified Theory / Low Background / Underground Experiment / Nonーaccelerator Physics
Research Abstract

1. Ultra-low background beta-ray and gamma-ray detectors ELEGANTS (ELEctron GAmma-ray NeuTrino Spectrometer) III, IV, V have been developed. By investigating double beta decays and other rare decay process, conservation laws, properties (mass, helicity) of neutrino and new particles have been studied.
2. ELE-III gave a lower limits of half lives : t>0.7X10^<23>years (y) and t > 0.6X10^<23>y for the neutrinoless double beta decays (0nubetabeta) of ^<76>Ge 0^+ -> 0^+ and 0^+ -> 2^+. The former was almost same level of other results and set limit of m_<nu>< 4eV on neutrino mass and the latter gave most stringent limit on the right-handed current.
3. ELE-IV gave a lower limit of t > 5.4 X 10^<18>y for two neutrino double beta decay (0nubetabeta) of ^<100>Mo. This was the most stringent limit at that time (1989).
4. ELE-V gave a finite value of tー1.5X10^<19>y for the 2nubetabeta of ^<100>Mo. This is the first result in the world by the counter method alone. It gives the 0nubetabeta nuclear matrix element. It gave the most stringent lower limit of t > 0.6X10^<22>y (m_<nu> <6eV) for the 0nu betabeta.
5.The sensitivity of the ELE-V is 10^<23>y for a half life of 0nubetabeta, corresponding to m_<nu> -1eV region.
6. Lower limits of t > 10^<20> - 10^<22>y for the double strangeness exchange weak decays (*S=2) NN->H (unddss) exclude the light H particle with the mass below 2m_N (1875MeV).
7. By using 0.77 ton of NaI detector in ELE-V, a lower limit of t > 0.6X10^<23>y was obtained for charge nonconserving nuclear excitation. It sets upper limits of 3X10^<-25> and 1.5X10^<-40> on branching ratio of charge nonconservation mediated by the weak boson and photon. A lower lmit of 3.2X10^<23>y (preliminary) on a half life of the Kーelectron annihilation or the violation of Pauli exclusion principle through L to K-shell transition was obtained. These results were most stringent test of the charge conservation.
8. A new region of spinーcoupled dark matter were surveyed.

  • Research Products

    (18 results)

All Other

All Publications (18 results)

  • [Publications] H.Ejiri et al.,: "Double beta decay of ^<76>Ge(0^+)to 0^+ and 2^+ states in ^<76>Ge studied by the betaーgamma coincidence method," J. Phys., Nucl. Phys. B(1987)839,. (1987)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] H.Ejiri,: "Neutrino mass studied by nuclear betaーgamma spectroscpy," Nucl.Phys.A478(1988)426,. A478. (1988)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] K.Okada et al.,: "Double beta decay measurements for ^<76>Ge and ^<100>Mo," Nucl.Phys.A478(1988)447,. A478. (1988)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] H.Ejiri et al.,: "Search for H dyhyperon by double weak decays of nuclei," Phys.Letters 228B(1989)24,. 228B. (1989)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] H.Ejiri,: "Double beta decays and related subject for particle and nuclear physics," Nucl.Phys.A(1991),. (1991)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] H.Ejiri et al.,: "High sensitive betaーgamma spectrometer ELEGANTSーV," Nucl.Instr.Methods(1991).(1991)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] H.Ejiri et al.,: "Low background measurements of neutrons by Ge detectors," Nucl.Instr.Methods(1991).(1991)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] H.Ejiri et al.,: "Double beta decay of ^<100>Mo," Phys.Letters(1991).(1991)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] H.Ejiri et al.,: "Double beta decay of ^<100>Mo and CNC excitation of ^<127>I," J.Phys.,Nucle.Phys.(1991).(1991)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] H. Ejiri: "Neutrino mass studied by nuclear beta-gamma spectroscopy," Nucl. Phys.A478. 1988 (426)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] K. Okada, et al.: "Double beta decay measurements for ^<76>Ge and ^<100>Mo," Nucl. Phys. A478. 1988 (447)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] H. Ejiri, et al.: "Search for the H dyhyperon by double weak decays of nuclei," Phys. Letters. 228B. 1989 (24)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] H. Ejiri,: "Double beta decays and related subject for particle and nuclear physics," Nucl. Phys.A. (1991)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] H. Ejiri et al.: "High sensitive beta-gamma spectrometer ELEGANTS-V," Nucl. Instr. Methods. (1991)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] H. Ejiri et al.: "Low background measurements of neutrons by Ge detectors," Nucl, Instr. Methods. (1991)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] H. Ejiri et al.: "Double beta decay of ^<100> Mo," Phys. Letters. (1991)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] H. Ejiri et al: "Double beta decay of ^<100> Mo and CNC excitation of ^<127>I," J. Phys., Nucle. Phys.(1991)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] H. Ejiri et al: "Double beta decay of ^<76>Ge(0^+) to 0^+ and 2^+ states in ^<76>Ge studied by the beta-gamma coincidence method." J. Phys., Nucl. Phys.B. 1987 (839)

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

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Published: 1993-08-12  

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