Observation of $t\bar{t}\gamma \gamma$ production at $\sqrt{s}=$13 TeV with the ATLAS detector

Abstract

This paper presents the first observation of top-quark pair production in association with two photons ($t\bar{t}\gamma \gamma$). The measurement is performed in the single-lepton decay channel using proton-proton collision data collected by the ATLAS detector at the Large Hadron Collider. The data correspond to an integrated luminosity of 140 fb${}^{-1}$ recorded during Run 2 at a centre-of-mass energy of 13 TeV. The $t\bar{t}\gamma \gamma$ production cross section, measured in a fiducial phase space based on particle-level kinematic criteria for the lepton, photons, and jets, is found to be $2.42_{-0.53}^{+0.58}\text{fb}$, corresponding to an observed significance of 5.2 standard deviations. Additionally, the ratio of the production cross section of $t\bar{t}\gamma \gamma$ to top-quark pair production in association with one photon is determined, yielding $(3.30_{-0.65}^{+0.70})\times 10^{-3}$.

38 pages in total, author list starting page 20, 3 figures, 1 table, published on Phys. Lett. B. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/TOPQ-2023-03