Observation of the doubly radiative decay $\hat{I}{\cdot }^{\prime }\to {\hat{I}}^3{\hat{I}}^3\ddot{I}{€}^0$

Abstract

Based on a sample of $1.31$ billion $J/\ddot{I}ˆ$ events collected with the BESIII detector, we report the study of the doubly radiative decay $\hat{I}{\cdot }^{\prime }\to {\hat{I}}^3{\hat{I}}^3\ddot{I}{€}^0$ for the first time, where the $\hat{I}{\cdot }^{\prime }$ meson is produced via the $J/\ddot{I}ˆ\to {\hat{I}}^3\hat{I}{\cdot }^{\prime }$ decay. The branching fraction of $\hat{I}{\cdot }^{\prime }\to {\hat{I}}^3{\hat{I}}^3\ddot{I}{€}^0$ inclusive decay is measured to be $\mathcal{B}(\hat{I}{\cdot }^{\prime }\to {\hat{I}}^3{\hat{I}}^3\ddot{I}{€}^0{)}_{\text{Incl.}}$ = $(3.20\pm0.07\mbox{(stat)}\pm0.23\mbox{(sys)})\times 10^{-3}$, while the branching fractions of the dominant process $\hat{I}{\cdot }^{\prime }\to {\hat{I}}^3\ddot{I}‰$ and the non-resonant component are determined to be ${\cal B}(η^\prime\to γω)\times {\cal B}(ω\to γπ^0) = (23.7 \pm1.4\mbox{(stat)}\pm1.8\mbox{(sys)})\times 10^{-4}$ and ${\cal B}(η^\prime\to γγπ^0)_{\text{NR}} = (6.16\pm0.64\mbox{(stat)} \pm0.67\mbox{(sys)})\times 10^{-4}$, respectively. In addition, the $M_{{\hat{I}}^3{\hat{I}}^3}^2$-dependent partial widths of the inclusive decay are also presented.