Measurement of the hyperon weak radiative decay $\Xi^0\to\gamma\Sigma^0$ at BESIII

Abstract

The hyperon weak radiative decay $\Xi^0\to\gamma\Sigma^0$ is measured via the process $J/\psi\to\Xi^0\bar\Xi^0$. The absolute branching fraction of $\Xi^0\to\gamma\Sigma^0$ is determined to be $(3.69\pm 0.21_{\text{stat}}\pm0.12_{\text{syst}})\times 10^{-3}$, based on $(10.087\pm 0.044)\times 10^{9}$ $J/\psi$ events collected with the BESIII detector operating at the BEPCII collider. The decay asymmetry parameter is measured, with a complete angular analysis of the cascade decay chain, to be $\alpha_{\gamma} = -0.807\pm 0.095_{\text{stat}}\pm 0.011_{\text{syst}}$.