Search for flavor-changing neutral current interactions of the top quark in final states with a photon and additional jets in proton-proton collisions at $\sqrt{s}$=13 TeV

A search for the production of a top quark in association with a photon and additional jets via flavor-changing neutral currents (FCNC) is presented. The analysis uses proton-proton collision data recorded by the CMS detector at a center-of-mass energy of $13~\mathrm{TeV}$, corresponding to an integrated luminosity of $138~\mathrm{fb}^{-1}$. The search is performed by looking for processes where a single top quark in association with a photon is produced through FCNC, or a pair of top quarks where one of the top quarks decays via FCNC interactions. Events with an electron or a muon, a photon, one or more jets, and missing transverse momentum are selected. Multivariate analysis techniques are used to discriminate signal and standard model background processes. No significant deviation is observed over the predicted standard model background. Observed (expected) upper limits are set on the branching fractions of top quark decays: $\mathcal{B}(\mathrm{t} \to \mathrm{u}+\gamma) < 0.95\times10^{-5}$ ($1.20\times10^{-5}$) and $\mathcal{B}(\mathrm{t} \to \mathrm{c}+\gamma) < 1.51\times10^{-5}$ ($1.54\times10^{-5}$) at $95\%$ confidence level, assuming one non-zero coupling at a time.