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 re...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.展开更多
To explain the anomALously large decay rate of ∑＋→p＋μ＋μ-, it was proposed that a new mechanism where a light CP-odd pseudoscaJar boson of mAo = 214.3 MeV makes a crucial contribution. Later, some authors have s...To explain the anomALously large decay rate of ∑＋→p＋μ＋μ-, it was proposed that a new mechanism where a light CP-odd pseudoscaJar boson of mAo = 214.3 MeV makes a crucial contribution. Later, some authors have studied the transition π0→e＋e- and γ→γA10 in terms of the same mechanism and their result indicates that with the suggested mass one cannot fit the data. This discrepancy might be caused by experimental error of ∑＋→p＋μ＋μ- because there were only a few events. Whether the mechanism is a reasonable one motivates us to investigate the transitions π0→e＋e-;η（η′）→μ＋μ-;ηc→μ＋μ-;ηb→τ＋τ- within the same framework. It is noted that for π0→ e＋ e-, the standard model （SM） prediction is smaller than the data, whereas the experimental central value of η→μ＋μ- is also above the SM prediction. It means that there should be extra contributions from other mechanisms and the contribution of A may be a possible one. Theoretically calculating the branching ratios of the concerned modes, we would cheek if we can obtain a univers mass for A10 which reconcile the theoretical predictions and data for all the modes. Unfortunately, we find that it is impossible conclude that the phenomenology does not favor such a to have such a mass with the same coupling｜gt｜. Therefore we light A10, even though a small window is still open.展开更多
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)+2 种基金support from the National Natural Science Foundation of China (12105006)Project funded by China Postdoctoral Science Foundation (2021M700343)China Postdoctoral Science Foundation (2021M690008)
文摘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.
基金Supported by the National Natural Science Foundation of China under Grant Nos.11075079and11005079the Special Grant for the Ph.D.Program of Ministry of Eduction of China No.20100032120065
文摘To explain the anomALously large decay rate of ∑＋→p＋μ＋μ-, it was proposed that a new mechanism where a light CP-odd pseudoscaJar boson of mAo = 214.3 MeV makes a crucial contribution. Later, some authors have studied the transition π0→e＋e- and γ→γA10 in terms of the same mechanism and their result indicates that with the suggested mass one cannot fit the data. This discrepancy might be caused by experimental error of ∑＋→p＋μ＋μ- because there were only a few events. Whether the mechanism is a reasonable one motivates us to investigate the transitions π0→e＋e-;η（η′）→μ＋μ-;ηc→μ＋μ-;ηb→τ＋τ- within the same framework. It is noted that for π0→ e＋ e-, the standard model （SM） prediction is smaller than the data, whereas the experimental central value of η→μ＋μ- is also above the SM prediction. It means that there should be extra contributions from other mechanisms and the contribution of A may be a possible one. Theoretically calculating the branching ratios of the concerned modes, we would cheek if we can obtain a univers mass for A10 which reconcile the theoretical predictions and data for all the modes. Unfortunately, we find that it is impossible conclude that the phenomenology does not favor such a to have such a mass with the same coupling｜gt｜. Therefore we light A10, even though a small window is still open.
