Evidence for $t\bar{t}t\bar{t}$ production in the multilepton final state in proton-proton collisions at $\sqrt{s}$=13 TeV with the ATLAS detector

TL;DR

This paper reports evidence for four-top-quark production in proton-proton collisions at 13 TeV using the ATLAS detector, employing multilepton final states and advanced analysis techniques to measure the production cross section.

Contribution

First evidence for four-top-quark production at the LHC with a detailed analysis of multilepton events and background constraints.

Findings

Measured cross section of 24^{+7}_{-6} fb for four-top-quark production.

Observed significance of 4.3 standard deviations, indicating evidence for the process.

Analysis techniques effectively distinguish signal from background in complex final states.

Abstract

A search is presented for four-top-quark production using an integrated luminosity of 139 fb$^{-1}$ of proton-proton collision data at a centre-of-mass energy of 13 TeV collected by the ATLAS detector at the LHC. Events are selected if they contain a same-sign lepton pair or at least three leptons (electrons or muons). Jet multiplicity, jet flavour and event kinematics are used to separate signal from the background through a multivariate discriminant, and dedicated control regions are used to constrain the dominant backgrounds. The four-top-quark production cross section is measured to be 24$^{+7}_{-6}$ fb. This corresponds to an observed (expected) significance with respect to the background-only hypothesis of 4.3 (2.4) standard deviations and provides evidence for this process.