1990 Fiscal Year Final Research Report Summary
Double Beta Decay and Neutrino
| Project/Area Number |
61065005
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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 | Osaka University |
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Principal Investigator |
EJIRI Hiroyasu Osaka Univ. Professor, 理学部, 教授 (80013374)
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| 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)
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| Project Period (FY) |
1986 – 1990
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| Keywords | Nucleus / Elementary Particle / Neutrino / Double Beta Decay / Ground Unified Theory / Low Background / Underground Experiment / Nonーaccelerator Physics |
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| 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.
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Research Products
(18 results)
