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

TL;DR

This paper reports the first observation of top-quark pair production with two photons at 13 TeV, measuring the cross section with high significance using ATLAS data, and comparing it to single-photon production.

Contribution

It provides the first measurement and observation of the $tar{t}\gamma\gamma$ process at the LHC, including cross section determination and ratio to single-photon production.

Findings

Measured cross section: 2.42 fb with uncertainties

Observed significance: 5.2 standard deviations

Cross section ratio: approximately 3.3 x 10^{-3}

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 $2.42^{+0.58}_{-0.53}\, \text{fb}$, 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 $(3.30^{+0.70}_{-0.65})\times 10^{-3}$.