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 $(3.69\pm 0.21_{\text{stat}}\pm 0.12_{\text{syst}})\times 10^{-3}$, 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 ${\alpha }_{\gamma }=-0.807\pm 0.095_{\text{stat}}\pm 0.011_{\text{syst}}$.