Search for the radiative decay $\eta \to \pi^0 \gamma \gamma$ in the SND experiment at VEPP-2M

TL;DR

This study searched for the rare decay $ ext{eta} o ext{pi}^0 ext{gamma} ext{gamma}$ using the SND detector at VEPP-2M, setting an upper limit on its branching ratio and reviewing related theoretical and experimental context.

Contribution

First experimental upper limit on the branching ratio of $ ext{eta} o ext{pi}^0 ext{gamma} ext{gamma}$ decay from the SND experiment, with detailed review for future research.

Findings

Upper limit on branching ratio: $8.4 imes 10^{-4}$ at 90% confidence level.

Results consistent with previous GAMS spectrometer measurements.

Provides detailed review to support future studies.

Abstract

The $\eta \to \pi^0 \gamma \gamma$ decay was investigated by the SND detector at VEPP-2M $e^+e^-$ collider in the reaction $e^+e^-\to\phi\to \eta\gamma$. Here we present the results and some details of this study. We report an upper limit (90% c.l.) $Br(\eta \to \pi^0 \gamma \gamma)<8.4\times 10^{-4}$ as our final result. Our upper limit does not contradict the earlier measurement by GAMS spectrometer. To facilitate future studies a rather detailed review of the problem is also given.