Measurement of the inclusive and differential $\mathrm{t}\bar{\mathrm{t}} + \gamma$ cross section and EFT interpretation in the single lepton channel at $\sqrt{s}=13~\mathrm{TeV}$

The production cross section of a top quark pair in association with a photon is measured in proton-proton collisions at the center-of-mass energy of $13~\mathrm{TeV}$. The data set of $137~\mathrm{fb}^{-1}$ was recorded by the CMS experiment during the LHC Run II. The measurement is performed in events with a well isolated, highly energetic lepton (electron or muon), with at least three jets from the hadronization of quarks and one isolated photon. The photon may be emitted from initial state radiation, from the top quarks, as well as from decay products of the top quarks. The analysis makes use of simultaneous likelihood fits in several signal and control regions to distinguish the $\mathrm{t}\bar{\mathrm{t}} + \gamma$ signal process from various backgrounds. The inclusive cross section for a photon with transverse momentum of $\mathrm{p}_\mathrm{T}\geq20~\mathrm{GeV}$ is measured as $800 \pm 46~\mathrm{(syst)} \pm 7~\mathrm{(stat)}~\mathrm{fb}$, in good agreement with the prediction from the standard model. The measurement is also carried out differentially in several kinematic observables and interpreted in the framework of the standard model effective field theory.