Observation of $\ddot{I}ˆ(3686)\to \hat{I}{\cdot }^{\prime }{e}^{+}{e}^{-}$

Abstract

Using a data sample of $448.1\times 10^6$ $\ddot{I}ˆ(3686)$ events collected with the BESIII detector at the BEPCII collider, we report the first observation of the electromagnetic Dalitz decay $\ddot{I}ˆ(3686)\to \hat{I}{\cdot }^{\prime }{e}^{+}{e}^{-}$, with significances of 7.0$\ddot{I}ƒ$ and 6.3$\ddot{I}ƒ$ when reconstructing the $\hat{I}{\cdot }^{\prime }$ meson via its decay modes $\hat{I}{\cdot }^{\prime }\to {\hat{I}}^3\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ and $\hat{I}{\cdot }^{\prime }\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}\hat{I}\cdot$ ($\hat{I}\cdot \to {\hat{I}}^3{\hat{I}}^3$), respectively. The weighted average branching fraction is determined to be $\mathcal{B}(\ddot{I}ˆ(3686)\to \hat{I}{\cdot }^{\prime }{e}^{+}{e}^{-})=(1.90\pm 0.25\pm 0.11)\times 10^{-6}$, where the first uncertainty is statistical and the second systematic.

10 pages, 3 figures