Search for the charged-lepton-flavor-violating decay $Z\to e\mu $ in $pp$ collisions at $\sqrt{s}=13\text{}\text{}\mathrm{TeV}$ with the ATLAS detector

A search for the charged-lepton-flavor-violating process $Z\to e\mu $ is presented, using $139\text{}\text{}{\mathrm{fb}}^{-1}$ of $\sqrt{s}=13\text{}\text{}\mathrm{TeV}$ $pp$ collision data collected by the ATLAS experiment at the LHC. An excess in the $e\mu $ invariant mass spectrum near the $Z$ boson mass would be a striking signature of new physics. No excess is observed, and an upper limit $B\left(Z\to e\mu \right)<2.62×{10}^{-7}$ is placed on the branching fraction at 95% confidence level, which is the most stringent limit to date.