Paper detail

Observation of $η^{\prime}\toωe^{+} e^{-}$

Based on a sample of \etapr mesons produced in the radiative decay $J/ψ\toγη^{\prime}$ in $1.31\times 10^9$ $J/ψ$ events collected with the BESIII detector, the decay $η^{\prime}\toωe^{+} e^{-}$ is observed for the first time, with a statistical significance of $8σ$. The branching fraction is measured to be $\mathcal{B}(η^{\prime}\toωe^{+} e^{-})=(1.97\pm0.34(\text{stat})\pm0.17(\text{syst}))\times10^{-4}$, which is in agreement with theoretical predictions. The branching fraction of $η^{\prime}\toωγ$ is also measured to be $(2.55\pm0.03(\text{stat})\pm0.16(\text{syst}))\times10^{-2}$, which is the most precise measurement to date, and the relative branching fraction $\frac{\mathcal{B}(η^{\prime}\to ωe^{+}e^{-})}{\mathcal{B}(η^{\prime}\to ωγ)}$ is determined to be $(7.71\pm1.34(\text{stat})\pm0.54(\text{syst}))\times10^{-3}$.