Study on Majorana nature of neutrinos in the inverted hierarchy region

2023 Fiscal Year Final Research Report

• Project Area: Unraveling the History of the Universe and Matter Evolution with Underground Physics
• Project/Area Number: 19H05803
• Research Category: Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)
• Allocation Type: Single-year Grants
• Review Section: Science and Engineering
• Research Institution: Tohoku University
• Principal Investigator: Inoue Kunio 東北大学, ニュートリノ科学研究センター, 教授 (10242166)
• Project Period (FY): 2019-06-28 – 2024-03-31
• Keywords: 二重ベータ崩壊 / マヨラナニュートリノ / 宇宙物質優勢 / 極低放射能 / 地球ニュートリノ

Outline of Final Research Achievements

We conducted a search for neutrinoless double beta decay in 136Xe with the world's highest sensitivity. The energy resolution was improved through detailed calibration and improved analysis methods, and the problem of the generation of long-lived radioactive nuclei due to cosmic rays was reduced by focusing on the number of associating neutrons. As a result, the excluded region on effective Majorana neutrino mass reached the inverted ordering region for the first time in the world, and started to cover theoretical predictions. Furthermore, in the geoneutrino observations that were being carried out in parallel as a multipurpose project, we succeeded in eliminating the High-Q model, which has a large amount of geothermal heat, and succeeded in providing new knowledge about the convection style and composition of the mantle. Neutrino observation has reached a new milestone in solving major problems in earth science.

Free Research Field

ニュートリノ実験

Academic Significance and Societal Importance of the Research Achievements

排除領域が逆階層領域や理論予想に切り込み始めたことで、「宇宙物質優勢の謎」といった根源的な疑問を解明できる可能性が一気に高まった。これを受け世界の探索計画は逆階層領域のカバーという方針に転換され、国際協働による統合や淘汰が進み、分野全体の底上げにつながった。また、地球ニュートリノ研究が地球科学に新たな知見をもたらし始めたことで、さらに挑戦的な観測プロジェクトが素粒子・地球科学の協働で提案されるなど、学際分野の活性化が進んだ。これら、知的好奇心を喚起するテーマにおいて世界をリードする研究を国内で進行させることで、優秀な若手の興味を引きつけ、科学立国日本の将来を担う人材発掘や育成に貢献した。