Search for the charged lepton flavor violating decay $\psi (3686)\to e^{\pm }{\mu }^{\mp }$

By analyzing $(2367.0\pm 11.1)\times {10}^6$ $\psi (3686)$ events collected in $e^{+}{e}^{-}$ collisions at $\sqrt{s}=3.686\mathrm{G}\mathrm{e}\mathrm{V}$ with the BESIII detector at the BEPCII collider, we report the first search for the charged lepton flavor violating decay $\psi (3686)\to e^{\pm }{\mu }^{\mp }$. No signal is found. An upper limit on the branching fraction $\mathcal{B}(\psi (3686)\to e^{\pm }{\mu }^{\mp })$ is determined to be $1.4\times {10}^{-8}$ at the 90% confidence level.