A search for leptoquark pair production decaying into
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Abstract or$$te^- \bar{t}e^+$$ in final states with multiple leptons is presented. The search is based on a dataset of$$t\mu ^- \bar{t}\mu ^+$$ pp collisions at recorded with the ATLAS detector during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb$$\sqrt{s}=13~\text {TeV} $$ . Four signal regions, with the requirement of at least three light leptons (electron or muon) and at least two jets out of which at least one jet is identified as coming from a$$^{-1}$$ b -hadron, are considered based on the number of leptons of a given flavour. The main background processes are estimated using dedicated control regions in a simultaneous fit with the signal regions to data. No excess above the Standard Model background prediction is observed and 95% confidence level limits on the production cross section times branching ratio are derived as a function of the leptoquark mass. Under the assumption of exclusive decays into ($$te^{-}$$ ), the corresponding lower limit on the scalar mixed-generation leptoquark mass$$t\mu ^{-}$$ is at 1.58 (1.59) TeV and on the vector leptoquark mass$$m_{\textrm{LQ}_{\textrm{mix}}^{\textrm{d}}}$$ at 1.67 (1.67) TeV in the minimal coupling scenario and at 1.95 (1.95) TeV in the Yang–Mills scenario.$$m_{{\tilde{U}}_1}$$ Free, publicly-accessible full text available August 1, 2025 -
A bstract A search for pair production of squarks or gluinos decaying via sleptons or weak bosons is reported. The search targets a final state with exactly two leptons with same-sign electric charge or at least three leptons without any charge requirement. The analysed data set corresponds to an integrated luminosity of 139 fb
− 1of proton-proton collisions collected at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC. Multiple signal regions are defined, targeting several SUSY simplified models yielding the desired final states. A single control region is used to constrain the normalisation of theWZ + jets background. No significant excess of events over the Standard Model expectation is observed. The results are interpreted in the context of several supersymmetric models featuring R-parity conservation or R-parity violation, yielding exclusion limits surpassing those from previous searches. In models considering gluino (squark) pair production, gluino (squark) masses up to 2.2 (1.7) TeV are excluded at 95% confidence level.Free, publicly-accessible full text available February 1, 2025 -
Free, publicly-accessible full text available January 1, 2025
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A bstract A search for supersymmetry targeting the direct production of winos and higgsinos is conducted in final states with either two leptons (
e orμ ) with the same electric charge, or three leptons. The analysis uses 139 fb− 1ofpp collision data at = 13 TeV collected with the ATLAS detector during Run 2 of the Large Hadron Collider. No significant excess over the Standard Model expectation is observed. Simplified and complete models with and without$$ \sqrt{s} $$ R -parity conservation are considered. In topologies with intermediate states including eitherWh orWZ pairs, wino masses up to 525 GeV and 250 GeV are excluded, respectively, for a bino of vanishing mass. Higgsino masses smaller than 440 GeV are excluded in a naturalR -parity-violating model with bilinear terms. Upper limits on the production cross section of generic events beyond the Standard Model as low as 40 ab are obtained in signal regions optimised for these models and also for anR -parity-violating scenario with baryon-number-violating higgsino decays into top quarks and jets. The analysis significantly improves sensitivity to supersymmetric models and other processes beyond the Standard Model that may contribute to the considered final states. -
A bstract A search for dark matter produced in association with a Higgs boson in final states with two hadronically decaying
τ -leptons and missing transverse momentum is presented. The analysis uses 139 fb− 1of proton-proton collision data at = 13 TeV collected by the ATLAS experiment at the Large Hadron Collider between 2015 and 2018. No evidence of physics beyond the Standard Model is found. The results are interpreted in terms of a 2HDM+$$ \sqrt{s} $$ a model featuring two scalar Higgs doublets and a pseudoscalar singlet field. Exclusion limits on the parameters of the model in selected benchmark scenarios are derived at 95% confidence level. Model-independent limits are also set on the visible cross-section for processes beyond the Standard Model producing missing transverse momentum in association with a Higgs boson decaying intoτ -leptons. -
A bstract This paper describes a search for the single production of an up-type vector-like quark (
T ) decaying asT →Ht orT →Zt . The search utilises a dataset ofpp collisions at = 13 TeV collected with the ATLAS detector during the 2015–2018 data-taking period of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb$$ \sqrt{s} $$ − 1. Data are analysed in final states containing a single lepton with multiple jets andb -jets. The presence of boosted heavy resonances in the event is exploited to discriminate the signal from the Standard Model background. No significant excess above the Standard Model expectation is observed, and 95% CL upper limits are set on the production cross section ofT quarks in different decay channels. The results are interpreted in several benchmark scenarios to set limits on the mass and universal coupling strength (κ ) of the vector-like quark. For singletT quarks,κ values above 0.53 are excluded for all masses below 2.3 TeV. At a mass of 1.6 TeV,κ values as low as 0.35 are excluded. ForT quarks in the doublet scenario, where the production cross section is much lower,κ values above 0.72 are excluded for all masses below 1.7 TeV, and this exclusion is extended toκ above 0.55 for low masses around 1.0 TeV. -
Abstract A search for pair-produced vector-like quarks using events with exactly one lepton (
e or ), at least four jets including at least one$$\mu $$ b -tagged jet, and large missing transverse momentum is presented. Data from proton–proton collisions at a centre-of-mass energy of 13$$\sqrt{s}=$$ , recorded by the ATLAS detector at the LHC from 2015 to 2018 and corresponding to an integrated luminosity of 139 fb$$\text {TeV}$$ , are analysed. Vector-like partners$$^{-1}$$ T andB of the top and bottom quarks are considered, as is a vector-likeX with charge , assuming their decay into a$$+5/3$$ W ,Z , or Higgs boson and a third-generation quark. No significant deviations from the Standard Model expectation are observed. Upper limits on the production cross-section ofT andB quark pairs as a function of their mass are derived for various decay branching ratio scenarios. The strongest lower limits on the masses are 1.59 assuming mass-degenerate vector-like quarks and branching ratios corresponding to the weak-isospin doublet model, and 1.47$$\text {TeV}$$ (1.46$$\text {TeV}$$ ) for exclusive$$\text {TeV}$$ ($$T \rightarrow Zt$$ ) decays. In addition, lower limits on the$$B/X \rightarrow Wt$$ T andB quark masses are derived for all possible branching ratios.