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

Abstract

The $\eta \to {\pi }^0\gamma \gamma$ decay was investigated by the SND detector at VEPP-2M $e^{+}{e}^{-}$ collider in the reaction $e^{+}{e}^{-}\to \varphi \to \eta \gamma$. 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.

Comments: 24 pages, 6 figures, LaTex. To be published in Nucl. Phys. B