Measurement of the $e^+e^-\to\eta\gamma$ cross section near the $\phi(1020)$ resonance with the SND detector

Abstract

In the experiment with the SND detector at the VEPP-2000 $e^+e^-$ collider, the $e^+e^-\to\eta\gamma$ cross section is measured in the energy range $E = 980 - 1060$ MeV. The measurement is carried out in the $\eta\to 2\gamma$ decay mode. Data with an integrated luminosity of 73 pb$^{-1}$ collected in 2018 and 2024 are used in the analysis. The measured cross section is the most accurate to date and is higher compared to other measurements. From the fit to the cross section data with the vector meson dominance model, the value of the product of the branching fractions $B(\phi\to e^+e^-)B(\phi\to \eta\gamma)$ has been obtained.