ATLAS projected sensitivities for for the cross-section measurement and new physics searches in four-top-quark production at the HL-LHC

This note presents projections for the study of four-top-quark production (pp tttt) at the High-Luminosity LHC (HL-LHC) using a dataset of up to 3~ab^-1 at s = 14~TeV. Two scenarios are explored to extrapolate theoretical and experimental systematic uncertainties from the current ATLAS measurement at 140~fb^-1. Sensitivity to the standard model cross section is evaluated, along with constraints on the top-quark Yukawa coupling and limits on Effective Field Theory operators. In addition, the search sensitivities to various heavy-resonance particles mediating tttt production are estimated. In the optimistic scenario, the expected uncertainty in the four-top production cross section is projected to be 6\%, while the 95\% confidence level upper limits on production cross-sections drop below 1~fb for heavy resonances with masses around or above 1~TeV.