Observation of four-top-quark production in the multilepton final state with the ATLAS detector

Abstract

This paper presents the observation of four-top-quark ($$t\bar{t}t\bar{t}$$ t t ¯ t t ¯ ) production in proton-proton collisions at the LHC. The analysis is performed using an integrated luminosity of 140 $$\hbox {fb}^{-1}$$ fb - 1 at a centre-of-mass energy of 13 TeV collected using the ATLAS detector. Events containing two leptons with the same electric charge or at least three leptons (electrons or muons) are selected. Event kinematics are used to separate signal from background through a multivariate discriminant, and dedicated control regions are used to constrain the dominant backgrounds. The observed (expected) significance of the measured $$t\bar{t}t\bar{t}$$ t t ¯ t t ¯ signal with respect to the standard model (SM) background-only hypothesis is 6.1 (4.3) standard deviations. The $$t\bar{t}t\bar{t}$$ t t ¯ t t ¯ production cross section is measured to be $$22.5^{+6.6}_{-5.5}$$ 22 . 5 - 5.5 + 6.6 fb, consistent with the SM prediction of $$12.0 \pm 2.4$$ 12.0 ± 2.4 fb within 1.8 standard deviations. Data are also used to set limits on the three-top-quark production cross section, being an irreducible background not measured previously, and to constrain the top-Higgs Yukawa coupling and effective field theory operator coefficients that affect $$t\bar{t}t\bar{t}$$ t t ¯ t t ¯ production.

Combining chromomagnetic and four-fermion operators with leading SMEFT operators for gg → hh at NLO QCD

“…[62] based on O(Λ −2 ) individual bounds or O(Λ −2 ) marginalised fits over the other Wilson coefficients. Meanwhile, constraints on 4-fermion operators in the 3rd generation also have been derived from the measurement of 4-top-quark production [102,103], based on fits varying each Wilson coefficient individually, however we use the more conservative ranges here. Note that, besides a flavour assumption, no a priori assumptions on the Wilson coefficients were made for the derivation of those limits, such that their ranges include values where the truncation at O(Λ −2 ) and/or our power counting may not be valid, i.e.…”

Quantum detection of new physics in top-quark pair production at the LHC

“…The top quark is the heaviest known fundamental particle, and its large coupling to the Higgs boson places it in a unique spot for the study of SM and BSM physics. Moreover, with order million top quarks produced per inverse femtobarn of luminosity, experiments at the LHC are able to perform a plethora of measurements involving top quarks, ranging from very detailed properties of t t and single-top production, to the observations of more rare processes such as associated production of electroweak bosons and recently even the simultaneous production of four top quarks [18,19]. It is particularly exciting to realise that thanks to the existence of a such broad range of experimental results, some of which with high statistics, we are also presented with the unique opportunity to probe the top sector with quantum observables.…”

Recent results in Standard Model Physics

“…The study of 4-top production, which probes important couplings and could see large enhancement in many BSM scenarios, has seen a lot of progress in 2023. The same-sign and multilepton channels which were released in a first iteration earlier and have the highest sensitivity were reanalized and lead to observation by both ATLAS and CMS [2,3], see Figure 5 for a summary.…”

“…The Standard Model (SM) of particle physics precisely predicts production cross sections over an impressive span of 15 orders of magnitude, all the way from recent total cross-section measurements [1] to the most rare processes under study today. Recent achievements include the observation of processes such as four-top-quark production [2,3], single-top-quark production in association with a photon 𝑡𝛾 [4], WW𝛾 [5], WZ𝛾 [6], W𝛾𝛾 production [7], and evidence of tWZ production [8]. These processes, today considered rare, may well evolve into domains of precision physics, similar to the progression from the Higgs discovery to the current extensive Higgs measurement precision program: Today's rare processes are tomorrow's precision physics.…”