First observation of the $\eta_{c}\to\Xi^{0} \bar{\Xi}^{0}$ decay

Abstract

Using $(10087\pm 44)\times 10^6$ $J/\psi$ events collected with the BESIII detector at the BEPCII collider, we report the first observation of the decay $\eta_{c} \to \Xi^{0} \bar{\Xi}^{0}$. The interference between $J/\psi\to\gamma\eta_c\to\gamma\Xi^0\bar{\Xi}^0$ and $J/\psi\to\gamma\Xi^0\bar{\Xi}^0|_{\rm non-resonance}$ is considered in the $\Xi^0 \bar{\Xi}^0$ mass spectrum fits. The branching fractions are measured to be $B(\eta_c \to \Xi^0 \bar{\Xi}^0)=(1.33 \pm 0.03 \pm 0.18) \times 10^{-3}$ for the constructive interference and $B(\eta_c \to \Xi^0 \bar{\Xi}^0)=(1.63 \pm 0.04 \pm 0.21) \times 10^{-3}$ for the destructive interference, where the first uncertainties are statistical and the second are systematic.