Search for the decay $\eta'\to\gamma\gamma\eta$

Abstract

Using a data sample of $1.31 × 10^9$ $J/\psi$ events collected with the BESIII detector, a search for $\eta'\to\gamma\gamma\eta$ via $J/\psi$ $\to$ $\gamma\eta'$ is performed for the first time. No significant $\eta'$ signal is observed in the $\gamma\gamma\eta$ invariant mass spectrum, and the branching fraction of $\eta'\to\gamma\gamma\eta$ is determined to be less than 1.33 × 10$^{−4}$ at the 90% confidence level.