The $\phi\to\eta\pi^0\gamma$ decay

TL;DR

This paper reports the measurement of the rare radiative decay $ o ext{ exteta} ext{ extpi}^0 ext{ extgamma}$, observing a significant contribution from the $a_0(980) ext{ extgamma}$ intermediate state, based on data from the SND detector at VEPP-2M.

Contribution

First measurement of the branching ratio for $ o ext{ exteta} ext{ extpi}^0 ext{ extgamma}$ decay with evidence of $a_0(980) ext{ extgamma}$ intermediate state contribution.

Findings

Branching ratio measured as $(0.88\pm0.14 ext{ extstat}) imes 10^{-4}$.

Significant contribution of $a_0(980) ext{ extgamma}$ intermediate state.

Data corresponds to $2 imes 10^7$ $$ mesons produced.

Abstract

Rare radiative decay $\phi\to\eta\pi^0\gamma$ was studied with SND detector at {VEPP-2M} electron-positron collider and its branching ratio was measured: $B(\phi\to\eta\pi^0\gamma)=(0.88\pm0.14\pm0.09)\cdot 10^{-4}$. Significant contribution of the $a_0(980)\gamma$ intermediate state was observed in the decay. The result is based on total integrated luminosity corresponding to $2\cdot10^7$ produced $\phi$ mesons.