Four top final states with NLO accuracy in perturbative QCD: 3 lepton channel

We examine the effect of higher-order QCD corrections on the four top-quark production cross section in the $3$ lepton decay channel. Top-quark and $W$ gauge-boson decays are included at next-to-leading order in perturbative QCD. The narrow-width approximation, that preserves spin correlations, is used to perform the calculation for this complex $2 \to 12 \,(13)$ process. We present differential cross-section distributions of top-quark decay products for the LHC Run III energy of $\sqrt{s}=13.6$ TeV, using realistic selection cuts. Our results show that QCD corrections and jet radiation in top-quark and $W$ decays can lead to significant changes in shapes of basic kinematic distributions and, therefore, need to be included for the accurate description of $pp \to t\bar{t}t\bar{t}+X$ process in the $3\ell$ decay channel. The NLO QCD results obtained in this work are important in the context of the recent observation of the $pp\to t\bar{t}t\bar{t}+X$ process by the ATLAS and CMS collaborations and are of great significance for the High-Luminosity phase of the LHC.