Study of the Process $${e}^{{+}}{e}^{{-}}{\to}{\eta\pi}^{{0}}{\gamma}$$ in the Cossision-Energy Range of $$\sqrt{{s}}{=}{1.05{-}2.00}$$ GeV

The process $$e^{+}e^{-}\to\eta\pi^{0}\gamma$$ is studied in the range of center-of-mass (c.m.) collision energies between 1.05 and 2.00 GeV on the basis of data corresponding to an integrated luminosity of 94.5 pb $${}^{-1}$$ that were accumulated in an experiment with the SND detector at the VEPP-2000 $$e^{+}e^{-}$$ collider. The cross section for this process was measured for the first time and was found to receive a dominant contribution from the mechanism of a transition through an $$\omega\eta$$ intermediate state. The cross section measured for the process $$e^{+}e^{-}\to\omega\eta\to\eta\pi^{0}\gamma$$ agrees with the results of earlier measurements in the channel $$e^{+}e^{-}\to\pi^{+}\pi^{-}\pi^{0}\eta$$ . At a level of 5.7 standard deviations (5.7 $$\sigma$$ ), it is established that the process $$e^{+}e^{-}\to\eta\pi^{0}\gamma$$ is not fully described by hadronic intermediate states of the $$VP$$ type. The cross section was measured for this missing contribution, which may be generated by radiative processes—for example, $$e^{+}e^{-}\to a_{0}(1450)\gamma$$ . It ranges from 15 to 20 pb over a broad energy interval extending from 1.3 to 1.9 GeV.