| 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)
上窪田 紀彦 大阪大学, 理学部, 学振特別研究員 (10183782)
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| Project Period (FY) |
1986 – 1990
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| Project Status |
Completed (Fiscal Year 1990)
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| Budget Amount *help |
¥267,800,000 (Direct Cost: ¥267,800,000)
Fiscal Year 1990: ¥5,000,000 (Direct Cost: ¥5,000,000)
Fiscal Year 1989: ¥5,000,000 (Direct Cost: ¥5,000,000)
Fiscal Year 1988: ¥5,000,000 (Direct Cost: ¥5,000,000)
Fiscal Year 1987: ¥175,500,000 (Direct Cost: ¥175,500,000)
Fiscal Year 1986: ¥77,300,000 (Direct Cost: ¥77,300,000)
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| Keywords | Nucleus / Elementary Particle / Neutrino / Double Beta Decay / Ground Unified Theory / Low Background / Underground Experiment / Nonーaccelerator Physics / 大統ー理論 / ニュートリノ / 宇宙暗黒物質 / 右巻弱相互作用 / 電子崩壊 / 電荷保存則 / H粒子 / ストレンジ物質 / ニュートリノ質量 / 二重ベータ崩壊 / ベータガンマニュートリノ核分光 / 弱相互作用右巻カレント / エレガントV号 / レプトン数非保存 / 大統-理論 / 極低バックグラウンド核分光 / ベータ・ガンマ精密核分光 |
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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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