# Precision Measurement of the Decay $\Sigma^{+} \rightarrow p\gamma$ in the Process $J/\psi\rightarrow \Sigma^{+}\bar{\Sigma}^{-}$

## TL;DR

This paper reports the first measurement of the $ ext{Sigma}^+
ightarrow p ext{gamma}$ decay in $J/\psi$ decays, providing the most precise values for its branching fraction and decay asymmetry parameter, with significant improvements over previous data.

## Contribution

First measurement of $ ext{Sigma}^+
ightarrow p ext{gamma}$ decay in $J/\psi$ decays, with highly precise branching fraction and asymmetry parameter values.

## Key findings

- Branching fraction measured as (0.996 ± 0.021 ± 0.018)×10^{-3}
- Decay asymmetry parameter determined as -0.652 ± 0.056 ± 0.020
- Results are the most precise to date, with significant improvements in accuracy.

## Abstract

Using $(10\:087\pm44)\times10^{6}$ $J/\psi$ events collected with the BESIII detector, the radiative hyperon decay $\Sigma\rightarrow p\gamma$ is studied at an electron-positron collider experiment for the first time. The absolute branching fraction is measured to be $\left(0.996 \pm 0.021_{\rm stat.}\pm 0.018_{\rm syst.}\right)\times 10^{-3}$, which is lower than its world average value by $4.2$ standard deviations. Its decay asymmetry parameter is determined to be $-0.652 \pm 0.056_{\rm stat.}\pm 0.020_{\rm syst.}$. The branching fraction and decay asymmetry parameter are the most precise to date, and the accuracies are improved by $78\%$ and $34\%$, respectively.