Observation of the electromagnetic Dalitz decay $D^{\ast 0}\to D^0{e}^{+}{e}^{-}$

Abstract

Based on 3.19 fb${}^{-1}$ of $e^{+}{e}^{-}$ collision data accumulated at the center-of-mass energy 4.178 GeV with the BESIII detector operating at the BEPCII collider, the electromagnetic Dalitz decay $D^{\ast 0}\to D^0{e}^{+}{e}^{-}$ is observed for the first time with a statistical significance of $13.2\ddot{I}ƒ$. The ratio of the branching fraction of $D^{\ast 0}\to D^0{e}^{+}{e}^{-}$ to that of $D^{\ast 0}\to D^0{\hat{I}}^3$ is measured to be $(11.08\pm 0.76\pm 0.49)\times 10^{-3}$. By using the world average value of the branching fraction of $D^{\ast 0}\to D^0{\hat{I}}^3$, the branching fraction of $D^{\ast 0}\to D^0{e}^{+}{e}^{-}$ is determined to be $(3.91\pm 0.27\pm 0.17\pm 0.10)\times 10^{-3}$, where the first uncertainty is statistical, the second systematic and the third external branching fractions.