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  1. Abstract

    A search for leptoquark pair production decaying into$$te^- \bar{t}e^+$$te-t¯e+or$$t\mu ^- \bar{t}\mu ^+$$tμ-t¯μ+in final states with multiple leptons is presented. The search is based on a dataset ofppcollisions at$$\sqrt{s}=13~\text {TeV} $$s=13TeVrecorded with the ATLAS detector during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb$$^{-1}$$-1. 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 ab-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$$te^{-}$$te-($$t\mu ^{-}$$tμ-), the corresponding lower limit on the scalar mixed-generation leptoquark mass$$m_{\textrm{LQ}_{\textrm{mix}}^{\textrm{d}}}$$mLQmixdis at 1.58 (1.59) TeV and on the vector leptoquark mass$$m_{{\tilde{U}}_1}$$mU~1at 1.67 (1.67) TeV in the minimal coupling scenario and at 1.95 (1.95) TeV in the Yang–Mills scenario.

     
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    Free, publicly-accessible full text available August 1, 2025
  2. A search for high-mass resonances decaying into aτ-lepton and a neutrino using proton-proton collisions at a center-of-mass energy ofs=13TeVis presented. The full run 2 data sample corresponding to an integrated luminosity of139fb1recorded by the ATLAS experiment in the years 2015–2018 is analyzed. Theτ-lepton is reconstructed in its hadronic decay modes and the total transverse momentum carried out by neutrinos is inferred from the reconstructed missing transverse momentum. The search for new physics is performed on the transverse mass between theτ-lepton and the missing transverse momentum. No excess of events above the Standard Model expectation is observed and upper exclusion limits are set on theWτνproduction cross section. HeavyWvector bosons with masses up to 5.0 TeV are excluded at 95% confidence level, assuming that they have the same couplings as the Standard ModelWboson. For nonuniversal couplings,Wbosons are excluded for masses less than 3.5–5.0 TeV, depending on the model parameters. In addition, model-independent limits on the visible cross section times branching ratio are determined as a function of the lower threshold on the transverse mass of theτ-lepton and missing transverse momentum.

    <supplementary-material><permissions><copyright-statement>© 2024 CERN, for the ATLAS Collaboration</copyright-statement><copyright-year>2024</copyright-year><copyright-holder>CERN</copyright-holder></permissions></supplementary-material></sec> </div> <a href='#' class='show open-abstract' style='margin-left:10px;'>more »</a> <a href='#' class='hide close-abstract' style='margin-left:10px;'>« less</a> <div class="actions" style="padding-left:10px;"> <span class="reader-count"> Free, publicly-accessible full text available June 1, 2025</span> </div> </div><div class="clearfix"></div> </div> </li> <li> <div class="article item document" itemscope itemtype="http://schema.org/TechArticle"> <div class="item-info"> <div class="title"> <a href="https://par.nsf.gov/biblio/10512851-atlas-experiment-cern-large-hadron-collider-description-detector-configuration-run3" itemprop="url"> <span class='span-link' itemprop="name">The ATLAS experiment at the CERN Large Hadron Collider: a description of the detector configuration for Run 3</span> </a> </div> <div> <strong> <a class="misc external-link" href="https://doi.org/10.1088/1748-0221/19/05/P05063" target="_blank" title="Link to document DOI">https://doi.org/10.1088/1748-0221/19/05/P05063  <span class="fas fa-external-link-alt"></span></a> </strong> </div> <div class="metadata"> <span class="authors"> <span class="author" itemprop="author">Aad, G</span> <span class="sep">; </span><span class="author" itemprop="author">Abbott, B</span> <span class="sep">; </span><span class="author" itemprop="author">Abbott, DC</span> <span class="sep">; </span><span class="author" itemprop="author">Abdallah, J</span> <span class="sep">; </span><span class="author" itemprop="author">Abeling, K</span> <span class="sep">; </span><span class="author" itemprop="author">Abidi, SH</span> <span class="sep">; </span><span class="author" itemprop="author">Aboulhorma, A</span> <span class="sep">; </span><span class="author" itemprop="author">Abovyan, S</span> <span class="sep">; </span><span class="author" itemprop="author">Abramowicz, H</span> <span class="sep">; </span><span class="author" itemprop="author">Abreu, H</span> <span class="sep">; </span><span class="author">et al</span></span> <span class="year">( <time itemprop="datePublished" datetime="2024-05-01">May 2024</time> , Journal of Instrumentation) </span> </div> <div style="cursor: pointer;-webkit-line-clamp: 5;" class="abstract" itemprop="description"> <title>Abstract

    The ATLAS detector is installed in its experimental cavern at Point 1 of the CERN Large Hadron Collider. During Run 2 of the LHC, a luminosity of  ℒ = 2 × 1034cm-2s-1was routinely achieved at the start of fills, twice the design luminosity. For Run 3, accelerator improvements, notably luminosity levelling, allow sustained running at an instantaneous luminosity of  ℒ = 2 × 1034cm-2s-1, with an average of up to 60 interactions per bunch crossing. The ATLAS detector has been upgraded to recover Run 1 single-lepton trigger thresholds while operating comfortably under Run 3 sustained pileup conditions. A fourth pixel layer 3.3 cm from the beam axis was added before Run 2 to improve vertex reconstruction and b-tagging performance. New Liquid Argon Calorimeter digital trigger electronics, with corresponding upgrades to the Trigger and Data Acquisition system, take advantage of a factor of 10 finer granularity to improve triggering on electrons, photons, taus, and hadronic signatures through increased pileup rejection. The inner muon endcap wheels were replaced by New Small Wheels with Micromegas and small-strip Thin Gap Chamber detectors, providing both precision tracking and Level-1 Muon trigger functionality. Trigger coverage of the inner barrel muon layer near one endcap region was augmented with modules integrating new thin-gap resistive plate chambers and smaller-diameter drift-tube chambers. Tile Calorimeter scintillation counters were added to improve electron energy resolution and background rejection. Upgrades to Minimum Bias Trigger Scintillators and Forward Detectors improve luminosity monitoring and enable total proton-proton cross section, diffractive physics, and heavy ion measurements. These upgrades are all compatible with operation in the much harsher environment anticipated after the High-Luminosity upgrade of the LHC and are the first steps towards preparing ATLAS for the High-Luminosity upgrade of the LHC. This paper describes the Run 3 configuration of the ATLAS detector.

     
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    Free, publicly-accessible full text available May 1, 2025
  3. A<sc>bstract</sc>

    A search for supersymmetry targeting the direct production of winos and higgsinos is conducted in final states with either two leptons (eorμ) with the same electric charge, or three leptons. The analysis uses 139 fb1ofppcollision data at$$ \sqrt{s} $$s= 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 withoutR-parity conservation are considered. In topologies with intermediate states including eitherWhorWZpairs, 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.

     
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  4. A<sc>bstract</sc>

    A search for dark matter produced in association with a Higgs boson in final states with two hadronically decayingτ-leptons and missing transverse momentum is presented. The analysis uses 139 fb1of proton-proton collision data at$$ \sqrt{s} $$s= 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+amodel 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.

     
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  5. Abstract

    A search for pair-produced vector-like quarks using events with exactly one lepton (eor$$\mu $$μ), at least four jets including at least oneb-tagged jet, and large missing transverse momentum is presented. Data from proton–proton collisions at a centre-of-mass energy of$$\sqrt{s}=$$s=13 $$\text {TeV}$$TeV, recorded by the ATLAS detector at the LHC from 2015 to 2018 and corresponding to an integrated luminosity of 139 fb$$^{-1}$$-1, are analysed. Vector-like partnersTandBof the top and bottom quarks are considered, as is a vector-likeXwith charge$$+5/3$$+5/3, assuming their decay into aW,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 ofTandBquark 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 $$\text {TeV}$$TeVassuming mass-degenerate vector-like quarks and branching ratios corresponding to the weak-isospin doublet model, and 1.47 $$\text {TeV}$$TeV(1.46 $$\text {TeV}$$TeV) for exclusive$$T \rightarrow Zt$$TZt($$B/X \rightarrow Wt$$B/XWt) decays. In addition, lower limits on theTandBquark masses are derived for all possible branching ratios.

     
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  6. A bstract A search for heavy Higgs bosons produced in association with a vector boson and decaying into a pair of vector bosons is performed in final states with two leptons (electrons or muons) of the same electric charge, missing transverse momentum and jets. A data sample of proton–proton collisions at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider between 2015 and 2018 is used. The data correspond to a total integrated luminosity of 139 fb − 1 . The observed data are in agreement with Standard Model background expectations. The results are interpreted using higher-dimensional operators in an effective field theory. Upper limits on the production cross-section are calculated at 95% confidence level as a function of the heavy Higgs boson’s mass and coupling strengths to vector bosons. Limits are set in the Higgs boson mass range from 300 to 1500 GeV, and depend on the assumed couplings. The highest excluded mass for a heavy Higgs boson with the coupling combinations explored is 900 GeV. Limits on coupling strengths are also provided. 
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