Study of the $\phi$ decays into $\pi^0\pi^0\gamma$ and $\eta\pi^0\gamma$ final states

TL;DR

This study measures the branching ratios of $$ radiative decays into $ ng$ and $ gg$ final states, revealing the dominance of the $f_0(980) o ext{mesons}$ mechanism and setting limits on $ ext{CP}$ violation in $ ext{eta}$ decays.

Contribution

First model-independent measurements of $$ radiative decay branching ratios into $ ng$ and $ gg$, highlighting the role of $f_0(980)$ in the decay process.

Findings

Branching ratio for $ o ng$ is approximately $0.92 imes 10^{-4}$.

Branching ratio for $ o gg$ is approximately $0.90 imes 10^{-4}$.

Dominance of $f_0(980) o ext{mesons}$ mechanism in $ o ng$ decay.

Abstract

Radiative decays of the $\phi$ meson have been studied using a data sample of about 19 million $\phi$ decays collected by the CMD-2 detector at VEPP-2M collider in Novosibirsk. From selected $e^+e^-\to\pi^{0}\pi^{0}\gamma$ and $e^+e^-\to\eta\pi^{0}\gamma$ events the following model independent results have been obtained: \par $Br(\phi\to\pi^{0}\pi^{0}\gamma) = (0.92\pm 0.08\pm0.06)\times10^{-4}$ for $M_{\pi^{0}\pi^{0}}>700$ MeV, \par $Br(\phi\to\eta\pi^{0}\gamma) = (0.90\pm 0.24\pm 0.10)\times10^{-4}$. It is shown that the intermediate mechanism $f_{0}(980)\gamma$ dominates in the $\phi\to\pi^{0}\pi^{0}\gamma$ decay and the corresponding branching ratio is \par $Br(\phi\to f_{0}(980)\gamma)=(2.90\pm 0.21\pm1.54)\times10^{-4}$. The systematic error is dominated by the possible model uncertainty. \par Using the same data sample the upper limit has been obtained for the P- and CP-violating decay of $\eta$ at 90% CL: \par $Br(\eta\to\pi^{0}\pi^{0}) < 4.3\times10^{-4}$ >.