Observation of $J/\psi $ decays to ${e}^{+}{e}^{-}{e}^{+}{e}^{-}$ and ${e}^{+}{e}^{-}{\mu }^{+}{\mu }^{-}$

Using a data sample of $4.481×{10}^{8}\text{}\text{}\psi \left(3686\right)$ events collected with the BESIII detector, we report the first observation of the four-lepton-decays $J/\psi \to {e}^{+}{e}^{-}{e}^{+}{e}^{-}$ and $J/\psi \to {e}^{+}{e}^{-}{\mu }^{+}{\mu }^{-}$ utilizing the process $\psi \left(3686\right)\to {\pi }^{+}{\pi }^{-}J/\psi $. The branching fractions are determined to be $\left[5.48±0.31\left(\mathrm{stat}\right)±0.45\left(\mathrm{syst}\right)\right]×{10}^{-5}$ and $\left[3.53±0.22\left(\mathrm{stat}\right)±0.13\left(\mathrm{syst}\right)\right]×{10}^{-5}$, respectively. The results are consistent with theoretical predictions. No significant signal is observed for $J/\psi \to {\mu }^{+}{\mu }^{-}{\mu }^{+}{\mu }^{-}$, and an upper limit on the branching fraction is set at $1.6×{10}^{-6}$ at the 90% confidence level. A $CP$ asymmetry observable is constructed for the first two channels, which is measured to be $\left(-0.012±0.054±0.010\right)$ and $\left(0.062±0.059±0.006\right)$, respectively. No evidence for $CP$ violation is observed in this process.