Explore the vast range of titles available.

A bstract This paper presents measurements of top-antitop quark pair ( t t ¯ ) production in association with additional b -jets. The analysis utilises 140 fb − 1 of proton–proton collision data collected with the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy of 13 TeV. Fiducial cross-sections are extracted in a final state featuring one electron and one muon, with at least three or four b -jets. Results are presented at the particle level for both integrated cross-sections and normalised differential cross-sections, as functions of global event properties, jet kinematics, and b -jet pair properties. Observable quantities characterising b -jets originating from the top quark decay and additional b -jets are also measured at the particle level, after correcting for detector effects. The measured integrated fiducial cross-sections are consistent with t t ¯ b b ¯ predictions from various next-to-leading-order matrix element calculations matched to a parton shower within the uncertainties of the predictions. State-of-the-art theoretical predictions are compared with the differential measurements; none of them simultaneously describes all observables. Differences between any two predictions are smaller than the measurement uncertainties for most observables.

A bstract The top-quark Yukawa coupling is extracted from the distribution of the top-quark pair ( t t ¯ ) invariant mass in proton-proton collisions using 140 fb − 1 of data at s = 13 TeV collected in 2015–2018 by the ATLAS experiment at the Large Hadron Collider. In the region near the production threshold, the t t ¯ invariant mass spectrum is sensitive to electroweak virtual corrections, including contributions from Higgs boson exchange, thereby providing sensitivity to the top-quark Yukawa coupling. This is the first measurement in ATLAS that aims to obtain this coupling exploiting this approach. The t t ¯ system is reconstructed in the single-lepton final state, requiring exactly one isolated electron or muon and at least four jets with at least two identified as originating from b -quarks. The measured Yukawa coupling is found to be in good agreement with the Standard Model prediction. An upper limit on the top-quark Yukawa coupling strength of Y t < 2 . 1 relative to the Standard Model prediction is observed at 95% confidence level, consistent with the expected sensitivity.

A search for a light charged Higgs boson pro duced in decays of the top quark, \\( t \\rightarrow H^\\pm b \\) with \\( H^\\pm \\rightarrow cs \\), is presented. This search targets the production of top-quark pairs \\( t\\bar{t} \\rightarrow WbH^\\pm b \\), with \\( W \\rightarrow \\ell\\nu \\) (\\( \\ell = e, \\mu \\)), resulting in a lepton-plus-jets final state characterised by an isolated electron or muon and at least four jets. The search exploits b-quark and c-quark identification techniques as well as multivariate methods to suppress the dominant \\( t\\bar{t} \\) background. The data analysed correspond to 140 fb\\(^{-1}\\) of pp collisions at \\( \\sqrt{s} = 13 \\) TeV recorded with the ATLAS detector at the LHC between 2015 and 2018. Observed (expected) 95% confidence-level upper limits on the branching fraction \\( B(t \\rightarrow H^\\pm b) \\), assuming \\( B(t \\rightarrow Wb) + B(t \\rightarrow H^\\pm(\\rightarrow cs)b) = 1.0 \\), are set between 0.066% (0.077%) and 3.6% (2.3%) for a charged Higgs boson with a mass between 60 and 168 GeV.

The top-quark Yukawa coupling is extracted from the distribution of the top-quark pair (tt̅) invariant mass in proton-proton collisions using 140 fb−1 of data at √s̅=13 TeV collected in 2015–2018 by the ATLAS experiment at the Large Hadron Collider. In the region near the production threshold, the tt̅ invariant mass spectrum is sensitive to electroweak virtual corrections, including contributions from Higgs boson exchange, thereby providing sensitivity to the top-quark Yukawa coupling. This is the first measurement in ATLAS that aims to obtain this coupling exploiting this approach. The tt̅ system is reconstructed in the single-lepton final state, requiring exactly one isolated electron or muon and at least four jets with at least two identified as originating from b-quarks. The measured Yukawa coupling is found to be in good agreement with the Standard Model prediction. An upper limit on the top-quark Yukawa coupling strength of Yt < 2.1 relative to the Standard Model prediction is observed at 95% confidence level, consistent with the expected sensitivity.

A bstract At the Large Hadron Collider, the WbWb final state is expected to be dominated by t t ¯ production with a contribution from single-top processes. Differential cross-sections for WbWb production in the dilepton decay channel are measured at the particle level as a function of various kinematic variables. The analysis is based on data from proton-proton collisions at a centre-of-mass energy of s = 13 TeV, recorded by the ATLAS detector at the Large Hadron Collider over the period from 2015 to 2018, corresponding to an integrated luminosity of 140 fb − 1 . Measurements are performed within the fiducial phase-space defined by the presence of two b -jets and one electron and one muon of opposite charges. The differential cross-sections are corrected for detector effects and unfolded to the particle level. Results are compared with predictions from Monte Carlo event generators at next-to-leading order in perturbative quantum chromodynamics; overall the measurements are in reasonable agreement with several generator setups, although no single prediction is able to describe all measured distributions simultaneously. These measurements provide valuable constraints on the modelling of WbWb production and the interference between doubly resonant and singly resonant WbWb production.

The top-quark Yukawa coupling is extracted from the distribution of the top-quark pair (t (t) over bar) invariant mass in proton-proton collisions using 140 fb(-1) of data at root s = 13TeV collected in 2015-2018 by the ATLAS experiment at the Large Hadron Collider. In the region near the production threshold, the t (t) over bar invariant mass spectrum is sensitive to electroweak virtual corrections, including contributions from Higgs boson exchange, thereby providing sensitivity to the top-quark Yukawa coupling. This is the first measurement in ATLAS that aims to obtain this coupling exploiting this approach. The t (t) over bar system is reconstructed in the single-lepton final state, requiring exactly one isolated electron or muon and at least four jets with at least two identified as originating from b-quarks. The measured Yukawa coupling is found to be in good agreement with the Standard Model prediction. An upper limit on the top-quark Yukawa coupling strength of Y-t < 2.1 relative to the Standard Model prediction is observed at 95% confidence level, consistent with the expected sensitivity.

This paper presents a search for physics beyond the Standard Model targeting a heavy resonance visible in the invariant mass of the lepton-jet system. The analysis focuses on final states with a high-energy lepton and jet, and is optimised for the resonant production of leptoquarks — a novel production mode mediated by the lepton content of the proton originating from quantum fluctuations. Four distinct and orthogonal final states are considered: e+light jet, μ+light jet, e+b-jet, and μ+b-jet, constituting the first search at the Large Hadron Collider for resonantly produced leptoquarks with couplings to electrons and muons. Events with an additional same-flavour lepton, as expected from higher-order diagrams in the signal process, are also included in each channel. The search uses proton-proton collision data from the full Run 2, corresponding to an integrated luminosity of 140 fb−1 at a centre-of-mass energy of √s̅=13 TeV, and from a part of Run 3 (2022–2023), corresponding to 55 fb−1 at √s̅=13.6 TeV. No significant excess over Standard Model predictions is observed. The results are interpreted as exclusion limits on scalar leptoquark (S̃1) production, substantially improving upon previous ATLAS constraints from leptoquark pair production for large coupling values. The excluded S̃1 S̃1 mass ranges depend on the coupling strength, reaching up to 3.4 TeV for quark-lepton couplings yde = 1.0, and up to 4.3 TeV, 3.1 TeV, and 2.8 TeV for ysμ, ybe, and ybμ couplings set to 3.5, respectively.

A search for single production of a vector-like quark Q, which could be either a singlet T, with charge ⅔, or a Y from a (T, B, Y) triplet, with charge -(4/3), is performed using data from proton-proton collisions at a centre-of-mass energy of 13 TeV. The data correspond to the full integrated luminosity of 140 fb−1 recorded with the ATLAS detector during Run 2 of the Large Hadron Collider. The analysis targets Q → Wb decays where the W boson decays leptonically. The data are found to be consistent with the expected Standard Model background, so upper limits are set on the cross-section times branching ratio, and on the coupling of the Q to the Standard Model sector for these two benchmark models. Effects of interference with the Standard Model background are taken into account. For the singlet T, the 95% confidence level limit on the coupling strength κ ranges between 0.22 and 0.52 for masses from 1150 to 2300 GeV. For the (T, B, Y) triplet, the limits on κ vary from 0.14 to 0.46 for masses from 1150 to 2600 GeV.

This paper presents measurements of top-antitop quark pair (\\( t\\bar{t} \\)) production in association with additional b-jets. The analysis utilises 140 fb\\(^{-1}\\) of proton–proton collision data collected with the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy of 13 TeV. Fiducial cross-sections are extracted in a final state featuring one electron and one muon, with at least three or four b-jets. Results are presented at the particle level for both integrated cross-sections and normalised differential cross-sections, as functions of global event properties, jet kinematics, and b-jet pair properties. Observable quantities characterising b-jets originating from the top quark decay and additional b-jets are also measured at the particle level, after correcting for detector effects. The measured integrated fiducial cross sections are consistent with \\( t\\bar{t}b\\bar{b} \\) predictions from various next-to-leading-order matrix element calculations matched to a parton shower within the uncertainties of the predictions. State of-the-art theoretical predictions are compared with the differential measurements; none of them simultaneously describes all observables. Differences between any two predictions are smaller than the measurement uncertainties for most observables.

A model-agnostic search for Beyond the Standard Model physics is presented, targeting final states with at least four light leptons (electrons or muons). The search regions are separated by event topology and unsupervised machine learning is used to identify anomalous events in the full 140 fb(-1) of proton-proton collision data collected with the ATLAS detector during Run 2. No significant excess above the Standard Model background expectation is observed. Model-agnostic limits are presented in each topology, along with limits on several benchmark models including vector-like leptons, wino-like charginos and neutralinos, or smuons. Limits are set on the flavourful vector-like lepton model for the first time.