Observation of t t ¯ γ γ production at s = 13 TeV with the ATLAS detector

UNSPECIFIED (2026) Observation of t t ¯ γ γ production at s = 13 TeV with the ATLAS detector. Phys Lett Sect B Nucl Elem Part High-Energy Phys. ISSN 0370-2693 (In Press)

Abstract

This paper presents the first observation of top-quark pair production in association with two photons ( t t ¯ γ γ ). 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 t ¯ γ γ 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 fb , corresponding to an observed significance of 5.2 standard deviations. Additionally, the ratio of the production cross section of t t ¯ γ γ to top-quark pair production in association with one photon is determined, yielding ( 3 . 30 − 0.65 + 0.70 ) × 10 − 3 .