| Project/Area Number |
13440081
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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 | The High Energy Accelerator Research Organization |
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Principal Investigator |
ISHIHARA Nobuhiro High Energy Accelerator Research Organization, Institute of Particle and Nuclear-Studies, Professor, 素粒子原子核研究所, 教授 (50044780)
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| Co-Investigator(Kenkyū-buntansha) |
TAMURA Norio Niigata University, Graduate School of Science and Technology, Professor, 大学院・自然科学研究科, 教授 (00025462)
YAMADA Yoshikazu High Energy Accelerator Research Organization, Institute of Particle and Nuclear Studies, Associate Professor, 素粒子原子核研究所, 助教授 (00200759)
INAGAKI Takao High Energy Accelerator Research Organization, Institute of Particle and Nuclear Studies, Professor, 素粒子原子核研究所, 教授 (60044757)
EMURA Tsuneo Tokyo University of Agriculture and Technology, Faculty of Technology, Professor, 工学部, 教授 (40015053)
KITAMURA Shoichi Tokyo Metropolitan University of Health Sciences, Faculty of Health Sciences, Professor, 保健科学部, 教授 (60106599)
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| Project Period (FY) |
2001 – 2003
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| Project Status |
Completed (Fiscal Year 2003)
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| Budget Amount *help |
¥14,300,000 (Direct Cost: ¥14,300,000)
Fiscal Year 2003: ¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2002: ¥4,300,000 (Direct Cost: ¥4,300,000)
Fiscal Year 2001: ¥6,400,000 (Direct Cost: ¥6,400,000)
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| Keywords | Double beta decay / Neutrino mass / Majorana neutrino / Drift chamber / Momentum analyzer / 運動量分析器 |
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| Research Abstract |
The existence of neutrino mass has been confirmed by the observation of neutrino oscillations. The next major matter of concern is to measure the absolute neutrino mass and to investigate that neutrinos are Majorana or Dirac particles. Because the small neutrino mass is naturally explained by the so-called see-saw mechanism, Majorana-type neutrino mass is theoretically expected. If neutrinos are Majorana particles, neutrinoless double beta decay takes place. In this situation, the present study of "Search for neutrinoless double beta decay with DCBA-T" was proposed.
A magnetic tracking detector, called Drift Chamber Beta-ray Analyzer (DCBA), consists of mini jet-type drift chambers and a solenoid magnet. Since this was the first plan to apply the drift chamber to double beta decay experiment in the world, a test apparatus called DCBA-T was constructed to solve technical problems. Effective neutrino mass, which is expected from the theoretical analysis based on the results of recent neut
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rino oscillation experiments, is in the order of 0.05 eV, depending on mass spectra. A detector having such mass sensitivity will require step-by-step processes in developing. DCBA-T is the first step, and having a mass sensitivity of about 4 eV. Tracks of two beta rays emitted from thin plates of decay source are detected by drift chambers, which are located in a uniform magnetic field. A momentum of each beta ray is obtained from a radius and a pitch angle of a helical track. Kinetic energy of each beta ray is also calculated from the momentum. A decay point is determined by two tracks. Since a drift chamber is insensitive to gamma rays, background events caused by gamma rays are effectively eliminated. DCBA-T confirmed that (1) the conversion electron track of 1 MeV from Br was obtained in the drift chamber filled with helium gas mixture at 1 atm, and (2) the electron energy was calculated from the momentum obtained from three dimensional track reconstruction. Now DCBA-T is engaged in searching for neutrinoless double beta decay events from the source of natural Nd_2O_3 containing 5.6% ^<150>Nd. On the other hand, improving the energy resolution is continued, as well as investigating the accommodation method for a large amount of source plates such as 600 kg of ^<150>Nd and ^<82>Se, in order to reach the mass sensitivity down to 0.05 eV. Less
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