Observation of the doubly radiative decay $\eta^{\prime}\to \gamma\gamma\pi^0$

Abstract

Based on a sample of 1.31 billion J/ψ events collected with the BESIII detector, we report the study of the doubly radiative decay η′→γγπ0 for the first time, where the η′ meson is produced via the J/ψ→γη′ decay. The branching fraction of η′→γγπ0 inclusive decay is measured to be B(η′→γγπ0)Incl. = (3.20±0.07(stat)±0.23(sys))×10−3, while the branching fractions of the dominant process η′→γω and the non-resonant component are determined to be B(η′→γω)×B(ω→γπ0)=(23.7±1.4(stat)±1.8(sys))×10−4 and B(η′→γγπ0)NR=(6.16±0.64(stat)±0.67(sys))×10−4, respectively. In addition, the Mγγ2-dependent partial widths of the inclusive decay are also presented.