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

TL;DR

This paper reports the first observation of the decay of the $ ext{eta}_c$ particle into $ ext{Xi}^0$ and anti-$ ext{Xi}^0$, measuring its branching fraction with high statistical significance.

Contribution

It provides the first experimental measurement of the $ ext{eta}_c o ext{Xi}^0 ar{ ext{Xi}}^0$ decay and accounts for interference effects in the analysis.

Findings

First observation of $ ext{eta}_c o ext{Xi}^0 ar{ ext{Xi}}^0$ decay.

Measured branching fractions around 1.3 to 1.6 per thousand.

Interference effects significantly influence the measured branching ratios.

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.