Extrapolation of ATLAS sensitivity to the measurement of the Standard Model four top quark cross section at the HL-LHC

This note presents projections for the measurement of the $pp \to t\bar{t}t\bar{t}$ cross section in the context of the High-Luminosity phase of the LHC with a dataset of up to 3000 $\textrm{fb}^{-1}$ at $\sqrt{s} = {14}$ TeV to be collected by the upgraded ATLAS detector. Several scenarios are studied for the extrapolation of theoretical and experimental systematic uncertainties from the 139 $\textrm{fb}^{-1}$ ATLAS measurement. In the most optimistic scenario, an expected signal significance of 6.4 standard deviations for the Standard Model process with respect to the background-only hypothesis and a cross section measurement uncertainty of 14% are obtained.