Measurement of the $t\bar{t}t\bar{t}$ production cross section in $pp$ collisions at $\sqrt{s}$=13 TeV with the ATLAS detector

TL;DR

This paper reports a measurement of the four-top-quark production cross section at 13 TeV using ATLAS data, employing multivariate analysis to distinguish signal from background, and finds results consistent with the Standard Model within uncertainties.

Contribution

First measurement of four-top-quark production cross section at 13 TeV with ATLAS, combining multiple analysis channels and advanced discrimination techniques.

Findings

Measured cross section: 24$^{+7}_{-6}$ fb.

Observed significance: 4.7 standard deviations.

Consistent with Standard Model predictions within 2 standard deviations.

Abstract

A measurement of four-top-quark production using proton-proton collision data at a centre-of-mass energy of 13 TeV collected by the ATLAS detector at the Large Hadron Collider corresponding to an integrated luminosity of 139 fb$^{-1}$ is presented. Events are selected if they contain a single lepton (electron or muon) or an opposite-sign lepton pair, in association with multiple jets. The events are categorised according to the number of jets and how likely these are to contain $b$-hadrons. A multivariate technique is then used to discriminate between signal and background events. The measured four-top-quark production cross section is found to be 26$^{+17}_{-15}$ fb, with a corresponding observed (expected) significance of 1.9 (1.0) standard deviations over the background-only hypothesis. The result is combined with the previous measurement performed by the ATLAS Collaboration in the multilepton final state. The combined four-top-quark production cross section is measured to be 24$^{+7}_{-6}$ fb, with a corresponding observed (expected) signal significance of 4.7 (2.6) standard deviations over the background-only predictions. It is consistent within 2.0 standard deviations with the Standard Model expectation of 12.0$\pm$2.4 fb.