2015 Fiscal Year Annual Research Report
ダークマター探索，二重ベータ崩壊及びエキゾチック原子核への精密原子核計算
| Project/Area Number |
14F04323
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| Research Institution | The University of Tokyo |
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Principal Investigator |
大塚 孝治 東京大学, 理学(系)研究科(研究院), 教授 (20201379)
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| Co-Investigator(Kenkyū-buntansha) |
MENENDEZ SANCHEZ JAVIER 東京大学, 理学(系)研究科(研究院), 外国人特別研究員
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| Project Period (FY) |
2014-04-25 – 2017-03-31
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| Keywords | Double-beta decay / Dark Matter scattering / Nuclear structure / Spectroscopy / Shell model / Chiral EFT / Three-nucleon forces / Meson-exchange currents |
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| Outline of Annual Research Achievements |
The detection of neutrinoless double-beta decay will establish that neutrinos are their own antiparticles but they will also unveil the unknown absolute neutrino mass if the nuclear matrix element (NME) of the transition is known. The research performed improved the precision of the NME calculations, and also studied the most important nuclear structure correlations needed for reliable NME calculations.
The nuclear structure input is crucial also for the interpretation of direct Dark Matter detection experiments which use nuclei as targets for the scattering of the Dark Matter particles. Dedicated studies of this process have been performed.
Finally, nuclear structure calculations based on chiral effective field theory (EFT) are able to provide controlled calculations with theoretical uncertainties. These have been explored in the present research.
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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
Two articles were published regarding neutrinoless double-beta decay. One, published in Physical Review Letters, improves previous NME calculations for 48Ca by extending the configuration space to two major shells. The impact is a 30% NME enhancement. In the second paper, published in Physical Review C, the importance of proton-neutron correlations, missing in some calculations, was highlighted.
Nuclear structure calculations were published in two articles. First, a review commissioned by the Annual Review of Nuclear and Particle Science journal summarizing the status of calculations for medium-mass nuclei with three-nucleon forces. Additionally an article published in Physical Review C presented new results covering the complete sd-shell.
Calculations have been performed for Dark Matter detection beyond the conventional approach, and they are being prepared for publication.
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| Strategy for Future Research Activity |
Nuclear Matrix Element (NME) for the neutrinoless double-beta decay have recently been calculated with two major shells within the shell model, and this type of the calculation can be extended to heavier isotopes like 76Ge, 82Se and 136Xe. The impact of these improved calculations will be high because the best experimental limits are presently obtained with these isotopes. On the other hand, the most relevant correlations for the decay will be further explored to understand the difference between different calculations. Finally, two-body currents will be included in all these decays.
Dark matter scattering off nuclei calculations will be completed covering the leading corrections to the standard case. These corrections are dictated by chiral EFT.
Finally, nuclear structure calculations with nuclear uncertainties will be attempted for heavier systems like nickel isotopes.
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