Weak radiative hyperon decays in covariant baryon chiral perturbation theory

TL;DR

This paper demonstrates that covariant baryon chiral perturbation theory, constrained by recent hyperon decay data, accurately describes weak radiative hyperon decays, resolving longstanding experimental and theoretical puzzles.

Contribution

The study applies covariant baryon chiral perturbation theory with new experimental constraints to successfully model weak radiative hyperon decays, aligning predictions with recent BESIII measurements.

Findings

Accurately describes BESIII data for $ ext{Λ} o n ext{γ}$ decays

Predicts branching fractions and asymmetry parameters consistent with experiments for $ ext{Ξ}^- o ext{Σ}^- ext{γ}$

Highlights importance of future measurements for testing theoretical predictions

Abstract

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 $\Lambda\to n\gamma$ by the BESIII Collaboration further exacerbate the issue, as none of the existing predictions can describe the data. We show in this letter 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 $\Xi^-\to\Sigma^-\gamma$ are also in agreement with the experimental data. We note that a more precise measurement of the asymmetry parameter, which is related with that of $\Sigma^+\to p\gamma$, is crucial to test Hara's theorem. We further predict the branching fraction and asymmetry parameter of $\Sigma^0\to n\gamma$, whose future measurement can serve as a highly nontrivial check on our understanding of weak radiative hyperon decay and on the covariant baryon chiral perturbation theory.