| Project/Area Number |
18K03669
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Multi-year Fund |
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| Section | 一般 |
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| Review Section |
Basic Section 15020:Experimental studies related to particle-, nuclear-, cosmic ray and astro-physics
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| Research Institution | Tohoku University (2019-2020)
The University of Tokyo (2018) |
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Principal Investigator |
Ichimura Koichi 東北大学, ニュートリノ科学研究センター, 助教 (80600064)
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| Project Period (FY) |
2018-04-01 – 2021-03-31
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| Project Status |
Completed (Fiscal Year 2020)
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| Budget Amount *help |
¥4,160,000 (Direct Cost: ¥3,200,000、Indirect Cost: ¥960,000)
Fiscal Year 2020: ¥390,000 (Direct Cost: ¥300,000、Indirect Cost: ¥90,000)
Fiscal Year 2019: ¥1,950,000 (Direct Cost: ¥1,500,000、Indirect Cost: ¥450,000)
Fiscal Year 2018: ¥1,820,000 (Direct Cost: ¥1,400,000、Indirect Cost: ¥420,000)
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| Keywords | ニュートリノ / 素粒子実験 / キセノン / 4重ベータ崩壊 / 4重電子捕獲 / 四重ベータ崩壊 / 四重電子捕獲 |
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| Outline of Final Research Achievements |
I have searched for the neutron-less quadruple beta decay of 136Xe in XMASS. The neutrino-less quadruple decay violates the lepton number, and the process can undergo even in the case that neutrino is a Dirac particle.XMASS is an 832 kg liquid xenon detector. Thanks to its low background event rate, and its capability of beta/gamma events separation, this neutrino-less quadruple beta decay search was conducted with high sensitivity.
No significant excess from the known background was observed and the first experimental constraint of the half-life of this decay mode was set. I reported this result at the JPS conference. The paper related to this research is under preparation. XMASS also has 124Xe isotopes that can undergo neutrino-less quadruple electron capture. To search for this process, I generated signal and background simulation data. This background simulation data can be used for other physics targets, such as dark matter searches using the whole XMASS data set.
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| Academic Significance and Societal Importance of the Research Achievements |
キセノンを用いた実験では世界中で暗黒物質探索やニュートリノを放出しない２重ベータ崩壊事象探索などが行われているが、本研究では液体キセノンの大発光量と自己遮蔽能による低放射能環境を活かし、新たにニュートリノを放出しない４重ベータ崩壊事象探索という新しい物理探索が可能であることを示すことが出来た。本研究で生成したXMASS検出器と周りの環境中の放射性物質に由来する雑音事象のシミュレーションデータは本研究以外にも応用可能であり、暗黒物質事象探索などに既に利用されている他、将来の探索感度向上のためにはどの放射性物質起源のバックグラウンドを低減しないといけないか、といった計画検討にも活用可能である。
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