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

## TL;DR

This study searches for the rare decay of eta prime into two photons and eta meson using a large dataset, setting an upper limit on its branching fraction due to no significant signal being observed.

## Contribution

First search for the decay mode $ ext{eta'} o ext{gamma} ext{gamma} ext{eta}$ using $J/ ext{psi}$ data with BESIII, establishing an upper limit on its branching fraction.

## Key findings

- No significant $ ext{eta'}$ signal observed.
- Upper limit on branching fraction set at $1.33 imes 10^{-4}$.
- First experimental constraint on this decay mode.

## Abstract

Using a data sample of $1.31\times10^{9} ~J/\psi$ 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 %upper limit of the branching fraction of $\eta'\to\gamma\gamma\eta$ is determined to be less than $1.33 \times 10^{-4}$ at the 90$\%$ confidence level.