Study of the process e+e-→ηπ0γ in the energy range s=1.05-2.00 GeV with the SND detector

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 ${\text{pb}}^{-1}$ 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.