Study of the process $e^+e^- \to \eta\pi^0\gamma$ in the energy range $\sqrt{s} = \mbox{1.05-2.00}$ GeV with the SND detector

TL;DR

This study measures the cross section of the process $e^+e^- o ext{eta} ext{pi}^0 ext{gamma}$ in the 1.05-2.00 GeV range, revealing dominant intermediate states and a significant contribution from radiation processes, using data from the SND detector.

Contribution

First measurement of the $e^+e^- o ext{eta} ext{pi}^0 ext{gamma}$ cross section in the 1.05-2.00 GeV range, identifying the dominant $ ext{omega} ext{eta}$ intermediate state and evidence of additional radiation contributions.

Findings

Dominant mechanism via $ ext{omega} ext{eta}$ intermediate state.

Measured cross section of the subprocess $e^+e^- o ext{omega} ext{eta}$.

Evidence of a radiation process contribution with a cross section of 15-20 pb from 1.3 to 1.9 GeV.

Abstract

The process $e^+e^-\to\eta\pi^0\gamma$ is studied in the center-of-mass energy range 1.05-2.00 GeV using data with an integrated luminosity of 94.5 pb$^{-1}$ collected by the SND detector at the VEPP-2000 $e^+e^-$ collider. The $e^+e^-\to\eta\pi^0\gamma$ cross section is measured for the first time. It is shown that the dominant mechanism of this reaction is the transition through the $\omega\eta$ intermediate state. The measured cross section of the subprocess $e^+e^-\to\omega\eta\to\eta\pi^0\gamma$ is consistent with previous measurements in the $e^+e^-\to\pi^+\pi^-\pi^0\eta$ mode. It is found, with a significance of 5.6$\sigma$, that the process $e^+e^-\to\eta\pi^0\gamma$ is not completely described by hadronic vector-pseudoscalar intermediate states. The cross section of this missing contribution, which can originate from radiation processes, e. g. $e^+e^-\to a_{0}(1450)\gamma$, is measured. It is found to be 15-20 pb in the wide energy range from 1.3 to 1.9 GeV.