2018 Fiscal Year Final Research Report
Analysis of positronium-xenon interaction in the ultra-low energy region for solving 'Xe puzzle'
| Project/Area Number |
16K17771
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| Research Category |
Grant-in-Aid for Young Scientists (B)
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| Allocation Type | Multi-year Fund |
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| Research Field |
Atomic/Molecular/Quantum electronics
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| Research Institution | The University of Tokyo |
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Principal Investigator |
Shibuya Kengo 東京大学, 大学院総合文化研究科, 助教 (20415425)
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| Research Collaborator |
SAITO haruo
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| Project Period (FY) |
2016-04-01 – 2019-03-31
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| Keywords | 陽電子 / ポジトロニウム / スピン転換反応 / スピン軌道相互作用 / キセノン / 原子分子散乱 / ガンマ線 / 部分波展開 |
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| Outline of Final Research Achievements |
Positronium (Ps) is a hydrogen-like atom consists of an electron and its anti-particle, i.e., a positron. The atom can be formed in many kinds of inert gases and the formation probability increases as the atomic number of the gas molecule increases. The exception is Xe gas in which the probability is only a few percent and it is called 'Xe puzzle' as the cause has been left unknown.
The author assumes that the Ps formation probability is not low in Xe, but it is underestimated because of another avenue for Ps quenching. The avenue has not been recognized for a long time, but it is open due to spin-orbit interaction converting the Ps spin states (from spin-triplet Ps to spin-singlet Ps).
The author examined this hypothesis from both sides of the experiments and simulations. The analysis was based on a partial-wave expansion method. As a result, the apparent value of Ps formation probability is found to be 2.8%, and the true one is found to be 29%. The 'Xe puzzle' is successfully solved.
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| Free Research Field |
陽電子物理、原子衝突
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| Academic Significance and Societal Importance of the Research Achievements |
実験と数値計算を駆使してPs形成率の真値を求めて上記「Xe問題」を解決するとともに、その背景にあるスピン転換反応や原子分子散乱の物理を明らかにした。
波及効果として（１）陽電子の生成から消滅に至る過程［銀河中心から放出されるガンマ線、PET（陽電子放射断層撮像）等］の理解に不可欠なPsと物質の相互作用の基礎データを示した。（２）多くの理論家が取り組むPs散乱のモデル計算の適否を判定する指針として期待される、散乱長、有効ポテンシャル、運動量移行断面積等の実験値を示した。（３）電磁量子力学の検証の系統的な不確かさの要因である、測定時のPsのエネルギー状態と真の平衡状態との乖離を見積もる基準を示した。
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