Observation of the Electromagnetic Dalitz Transition $h_c\to e^{+}{e}^{-}\hat{I}{\cdot }_c$

Abstract

Using $(27.12\pm 0.14)\times 10^8$ $\ddot{I}ˆ(3686)$ decays and data samples of $e^{+}{e}^{-}$ collisions with $\sqrt{s}$ from 4.130 to 4.780~GeV collected with the BESIII detector, we report the first observation of the electromagnetic Dalitz transition $h_c\to e^{+}{e}^{-}\hat{I}{\cdot }_c$ with a statistical significance of $5.4\ddot{I}ƒ$. We measure the ratio of the branching fractions $\frac{\mathcal{B}(h_c\to e^{+}{e}^{-}\hat{I}{\cdot }_c)}{\mathcal{B}(h_c\to {\hat{I}}^3\hat{I}{\cdot }_c)}$ separately for the $h_c$ samples produced via $\ddot{I}ˆ(3686)\to \ddot{I}{€}^0{h}_c$ and $e^{+}{e}^{-}\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}{h}_c$. The average ratio is determined to be $(0.59\pm 0.10(\text{stat.})\pm 0.04(\text{syst.}))\%$, where the uncertainty includes both statistical and systematic components.