Prospects for the measurement of $t\bar{t}\gamma$ with the upgraded ATLAS detector at the High-Luminosity LHC

Measurements of $t\bar{t}\gamma$ production are studied in leptonic final states at the HL-LHC, where a data set with an integrated luminosity of 3 ab$^{-1}$ at a center-of-mass energy of 14 TeV is expected to be collected by the upgraded ATLAS detector. The expected precisions for the measurements of both fiducial and differential cross-sections are presented. The fiducial cross-section measurement can reach an uncertainty as low as 6% (3%) in the channel with one (two) lepton(s) and requiring a photon candidate with transverse momentum larger than 20 GeV. This uncertainty increases to 8% (12%) for photons with transverse momentum above 500 GeV. The uncertainty of differential cross-section measurements, normalised to unity, for several typical observables is in general below 5%.