摘要
Weak radiative hyperon decays,important to test the strong interaction and relevant in searches for beyond the standard model physics,have remained puzzling both experimentally and theoretically for a long time.The recently updated branching fraction and first measurement of the asymmetry parameter of Λ→nγ by the BESIII Collaboration further exacerbate the issue,as none of the existing predictions can describe the data.We show in this work that the covariant baryon chiral perturbation theory,with constraints from the latest measurements of hyperon non-leptonic decays,can well describe the BESIII data.The predicted branching fraction and asymmetry parameter for Ξ→Σγ are also in agreement with the experimental data.We note that a more precise measurement of the asymmetry parameter,which is strongly constrained by chiral symmetry and related with that of Σ→pγ,is crucial to test Hara’s theorem.We further predict the branching fraction and asymmetry parameter of Σ~0→nγ,whose future measurement can serve as a highly nontrivial check on our understanding of weak radiative hyperon decays and on the covariant baryon chiral perturbation theory.
弱辐射超子衰变是少有的同时涉及强、弱和电磁3种相互作用的独特物理过程.这个看似简单的两体衰变,由于长久以来实验测量和理论预言存在较大差异,一直是粒子物理研究的难点问题之一,被称为弱辐射超子衰变疑难.近期,北京正负电子对撞机上的BESIII合作组首次测量了Λ→nγ衰变的不对称参数,更新了其衰变分支比,发现已有的理论预言都不能解释新的实验数据,这进一步加剧了弱辐射超子衰变疑难问题.本文在协变手征微扰理论的框架下,采用拓展的质量在壳重整化方案实现自洽的记阶规则,首次考虑了接触项树图贡献,通过拟合最新超子非轻衰变的实验数据确定理论的相关输入,系统研究了全部6个弱辐射(八重态)超子衰变道,结果显示协变手征微扰理论不仅能够很好地描述最新的BESIII实验数据,并且对4个有观测结果的弱辐射超子衰变道也能描述的较好.理论预言仅在∑^(+)→pγ衰变道与实验数据存在一定偏差.考虑到手征微扰理论的模型无关特性,作者鼓励实验物理学家在未来精确测量Ξ^(-)→Σ~-γ衰变道,以检验当前关于∑^(+)→pγ衰变的实验数据是否可靠,从而进一步加深对弱辐射超子衰变疑难的理解.此外,本研究也为超子稀有半轻衰变B→Bll中的新物理研究提供了必要的标准模型输入.
作者
Rui-Xiang Shi
Shuang-Yi Li
Jun-Xu Lu
Li-Sheng Geng
史瑞祥;李双一;陆俊旭;耿立升(School of Space and Environment,Beihang University,Beijing 102206,China;School of Physics,Beihang University,Beijing 102206,China;Peng Huanwu Collaborative Center for Research and Education,Beihang University,Beijing 100191,China;Beijing Key Laboratory of Advanced Nuclear Materials and Physics,Beihang University,Beijing 100191,China;School of Physics and Microelectronics,Zhengzhou University,Zhengzhou 450001,China)
基金
supported in part by the National Natural Science Foundation of China (11735003, 11975041, and11961141004)
support from the National Natural Science Foundation of China (12147145)
support from the National Natural Science Foundation of China (12105006)
Project funded by China Postdoctoral Science Foundation (2021M700343)
China Postdoctoral Science Foundation (2021M690008)
