Weak radiative hyperon decays in covariant baryon chiral perturbation theory

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.

Discriminating 1D new physics solutions in b→slldecays

The recent measurements of RK^(+),R_(K_(S)^(O)),RK^(*+),Bs→μ+μ-,a set of CP-averaged angular observables for the B^(0)→K^(*0)μ^(+)μ^(-)decay and its isospin partner B^(+)→K^(*+)μ^(+)μ^(-)by the LHCb Collaboration consistently hint at lepton universality violation in the b→sll transitions.In this work,we first perform global fits to the b→sll data and show that five one-dimensional scenarios,i.e,δC_(9)^(μ),δC_(10)^(μ),δC_(L)^(μ),δC_(9)^(μ)=C_(10)^(μ’),andδC_(9)^(μ)=-C_(9)^(μ’)can best explain the so-called B anamolies.Furthermore,we explore how these scenarios can be distinguished from each other.For this purpose,we first study the combinations of four angular asymmetries Ai(i=3,4,5,9)and find that they cannot distinguish the five new physics scenarios.We then show that a newly constructed ratio RS can uniquely discriminate the five new physics scenarios in proper intervals of q^(2) if it can be measured with percent-level precision.