Measurement of the relative probability of φ →ηγ decay in the η → π +π−π0 channel

The relative decay probability B(φ → ηγ) = (1.259 ± 0.030 ± 0.059)% in the decay channel η → π+π−π0 has been measured in an experiment using a spherical neutral detector in the VEPP-2M electron-positron storage ring. The result agrees with the tabulated value and with measurements of this probability using the spherical neutral detector in other η-meson decay channels.