Observation of the Dalitz Decay $D_s^{\ast +}\to D_s^{+}{e}^{+}{e}^{-}$

Abstract

Using 586 ${\text{pb}}^{-1}$ of $e^{+}{e}^{-}$ collision data acquired at $\sqrt{s}=4.170$ GeV with the CLEO-c detector at the Cornell Electron Storage Ring, we report the first observation of $D_s^{\ast +}\to D_s^{+}{e}^{+}{e}^{-}$ with a significance of $5.3\ddot{I}ƒ$. The ratio of branching fractions $\calB(D_{s}^{*+} \to D_{s}^{+} e^{+} e^{-}) / \calB(D_{s}^{*+} \to D_{s}^{+} γ)$ is measured to be $[0.72_{-0.13}^{+0.15}(\text{stat})\pm 0.10(\text{syst})]$, which is consistent with theoretical expectations.