Measurement of the branching fraction and decay asymmetry of $\Lambda\to n\gamma$

Abstract

The radiative hyperon decay $\Lambda\to n\gamma$ is studied using $(10087\pm44)\times 10^6$ $J/\psi$ events collected with the BESIII detector operating at BEPCII. The absolute branching fraction of the decay $\Lambda\to n\gamma$ is determined with a significance of 5.6$\sigma$ to be $[0.832\pm0.038(\rm stat.)\pm0.054(\rm syst.)]\times10^{-3}$, which lies significantly below the current PDG value. By analyzing the joint angular distribution of the decay products, the first determination of the decay asymmetry $\alpha_{\gamma}$ is reported with a value of $-0.16\pm0.10(\rm stat.)\pm0.05(\rm syst.)$.