Search for charged lepton flavor violation in top quark production and decay in proton-proton collisions at $\sqrt{s}=13~\mathrm{TeV}$

The result of a search for charged lepton flavor violation (CLFV) through top quark production and decay in proton-proton collisions at a center-of-mass energy of $13~\mathrm{TeV}$ is presented. The search is performed in events with an oppositely charged electron-muon pair in the final state along with at least one jet identified as originating from a bottom quark. The data correspond to an integrated luminosity of $137~\mathrm{fb}^{-1}$, collected by the CMS experiment at the CERN LHC in $2016$$-$$2018$. The CLFV interactions of top quarks are parametrized using an effective field theory (EFT) approach. In this analysis, we emphasize the importance of single top quark production via CLFV interactions, in addition to the t$\rightarrow$ e$\mu$q (q = u, c) decays. No significant excess over the standard model expectation is observed. The results are interpreted in terms of scalar-, vector- and tensor-like CLFV four-fermion EFT interactions. Exclusion limits at $95\%$ confidence level on the branching fractions of a top quark decaying to an e$\mu$ pair and an up (a charm) quark are found to be $0.12\times 10^{-6}$ ($1.59\times 10^{-6}$), $0.24\times 10^{-6}$ ($2.55\times 10^{-6}$), $0.46\times 10^{-6}$ ($4.62\times 10^{-6}$) for the scalar, vector and tensor CLFV interaction types, respectively.