Introduction

The most abundant and well known all-neutral $\phi$ and $\omega$ decays are $\phi$ -$>$ $\eta \gamma$ $(3\gamma)$ and $\omega$ -$>$ $\pi^0 \gamma$ (3$\gamma$). They are both 3$\gamma$ events and they can be used to check the calibration of the Lead Glass Detector (LGD). To examine 3$\gamma$ events, the invariant mass of every 2$\gamma$ pair in 3-cluster events is formed. The plot of 2$\gamma$ invariant mass shows two peaks one high and sharp corresponding to the $\pi ^0$ and one less pronounced near the $\eta$ mass. This is used to select desired $\phi$ or $\omega$ events, since $\pi ^0$ can come from $\omega$ decay while $\eta$ is expected from $\phi$ decay.