# A theoretical analysis of the doubly radiative decays $\eta^{(\prime)}\to\pi^0\gamma\gamma$ and $\eta^\prime\to\eta\gamma\gamma$

## TL;DR

This paper provides a theoretical analysis of specific eta meson radiative decay processes using the Linear Sigma Model and Vector Meson Dominance, predicting spectra and branching ratios and comparing them with experimental data.

## Contribution

It introduces a combined theoretical approach to analyze eta meson decays, offering new predictions for decay spectra and branching ratios, including recent experimental results.

## Key findings

- Successful modeling of decay spectra shapes
- Inability to simultaneously reproduce branching ratios
- First theoretical prediction for BESIII measurement

## Abstract

The scalar and vector meson exchange contributions to the doubly radiative decays $\eta^{(\prime)}\to\pi^0\gamma\gamma$ and $\eta^\prime\to\eta\gamma\gamma$ are analysed within the Linear Sigma Model and Vector Meson Dominance frameworks, respectively. Predictions for the diphoton invariant mass spectra and the associated integrated branching ratios are given and compared with current available experimental data. Whilst a satisfactory description of the shape of the $\eta\to\pi^{0}\gamma\gamma$ and $\eta^\prime\to\pi^{0}\gamma\gamma$ decay spectra is obtained, thus supporting the validity of the approach, the corresponding branching ratios cannot be reproduced simultaneously. A first theoretical prediction for the recently measured $\eta^\prime\to\eta\gamma\gamma$ by the BESIII collaboration is also presented.