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    237 research outputs found

    Letter to the editor

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    Crossref

    Author Correction: A detailed map of Higgs boson interactions by the ATLAS experiment ten years after the discovery

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    Crossref
    Archivio della Ricerca - Università di Pisa

    Determination of the parton distribution functions of the proton from ATLAS measurements of differential W± and Z boson production in association with jets

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    This article presents a new set of proton parton distribution functions, ATLASepWZVjet20, produced in an analysis at next-to-next-to-leading order in QCD. The new data sets considered are the measurements of W + and W − boson and Z boson production in association with jets in pp collisions at √ s = 8 TeV performed by the ATLAS experiment at the LHC with integrated luminosities of 20.2 fb−1 and 19.9 fb−1 , respectively. The analysis also considers the ATLAS measurements of differential W ± and Z boson production at √ s = 7 TeV with an integrated luminosity of 4.6 fb−1 and deep-inelastic-scattering data from e ± p collisions at the HERA accelerator. An improved determination of the sea-quark densities at high Bjorken x is shown, while confirming a strange-quark density similar in size to the up- and down-sea-quark densities in the range x . 0.02 found by previous ATLAS analyses
    University of Liverpool Repository
    Pontificia Universidad Católica de Chile: Repositorio UC
    Universidade do Minho: RepositoriUM
    Directory of Open Access Journals
    Repositorio Institucional Universidad de Granada
    The University of Arizona
    Digitala Vetenskapliga Arkivet - Academic Archive On-line
    Enlighten
    Queen Mary Research Online
    İstanbul Üniversitesi Açık Erişim Sistemi
    Adelaide Research & Scholarship
    Publikationer från Uppsala Universitet
    UCL Discovery
    eScholarship - University of California
    Radboud Repository (Radboud Univ.)
    Apollo (Cambridge)
    Lancaster E-Prints
    Archivio della ricerca- Università di Roma La Sapienza
    Swepub

    Search for supersymmetry in events with four or more charged leptons in 139 fb−1 of √s = 13 TeV pp collisions with the ATLAS detector

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    A search for supersymmetry in events with four or more charged leptons (electrons, muons and τ -leptons) is presented. The analysis uses a data sample corresponding to 139 fb−1 of proton-proton collisions delivered by the Large Hadron Collider at √ s = 13 TeV and recorded by the ATLAS detector. Four-lepton signal regions with up to two hadronically decaying τ -leptons are designed to target several supersymmetric models, while a general five-lepton signal region targets any new physics phenomena leading to a final state with five charged leptons. Data yields are consistent with Standard Model expectations and results are used to set upper limits on contributions from processes beyond the Standard Model. Exclusion limits are set at the 95% confidence level in simplified models of general gauge-mediated supersymmetry, excluding higgsino masses up to 540 GeV. In R-parity-violating simplified models with decays of the lightest supersymmetric particle to charged leptons, lower limits of 1.6 TeV, 1.2 TeV, and 2.5 TeV are placed on wino, slepton and gluino masses, respectively
    University of Liverpool Repository
    Pontificia Universidad Católica de Chile: Repositorio UC
    Universidade do Minho: RepositoriUM
    Ezid
    Directory of Open Access Journals
    Repositorio Institucional Universidad de Granada
    The University of Arizona
    Digitala Vetenskapliga Arkivet - Academic Archive On-line
    Enlighten
    Queen Mary Research Online
    İstanbul Üniversitesi Açık Erişim Sistemi
    MPG.PuRe
    Publikationer från Uppsala Universitet
    UCL Discovery
    eScholarship - University of California
    Radboud Repository (Radboud Univ.)
    Apollo (Cambridge)
    Lancaster E-Prints
    Archivio della ricerca- Università di Roma La Sapienza
    Swepub

    A search for the decays of stopped long-lived particles at √s = 13 TeV with the ATLAS detector

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    A search for long-lived particles, which have come to rest within the ATLAS detector, is presented. The subsequent decays of these particles can produce high-momentum jets, resulting in large out-of-time energy deposits in the ATLAS calorimeters. These de- cays are detected using data collected during periods in the LHC bunch structure when collisions are absent. The analysed dataset is composed of events from proton-proton collisions produced by the Large Hadron Collider at a centre-of-mass energy of s√ = 13 TeV and recorded by the ATLAS experiment during 2017 and 2018. The dataset used for this search corresponds to a total live time of 579 hours. The results of this search are used to derive lower limits on the mass of gluino R-hadrons, assuming a branching fraction B(g∼→qq¯¯χ01) = 100%, with masses of up to 1.4 TeV excluded for gluino lifetimes of 10−5 to 103 s
    University of Liverpool Repository
    Pontificia Universidad Católica de Chile: Repositorio UC
    Universidade do Minho: RepositoriUM
    Directory of Open Access Journals
    Repositorio Institucional Universidad de Granada
    The University of Arizona
    Digitala Vetenskapliga Arkivet - Academic Archive On-line
    Enlighten
    Queen Mary Research Online
    İstanbul Üniversitesi Açık Erişim Sistemi
    Adelaide Research & Scholarship
    Publikationer från Uppsala Universitet
    UCL Discovery
    eScholarship - University of California
    Radboud Repository (Radboud Univ.)
    Apollo (Cambridge)
    Lancaster E-Prints
    Archivio della ricerca- Università di Roma La Sapienza
    Explore Bristol Research

    Expected tracking performance of the ATLAS Inner Tracker at the High-Luminosity LHC

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    The high-luminosity phase of LHC operations (HL-LHC), will feature a large increase in simultaneous proton-proton interactions per bunch crossing up to 200, compared with a typical leveling target of 64 in Run 3. Such an increase will create a very challenging environment in which to perform charged particle trajectory reconstruction, a task crucial for the success of the ATLAS physics program, and will exceed the capabilities of the current ATLAS Inner Detector (ID). A new all-silicon Inner Tracker (ITk) will replace the current ID in time for the start of the HL-LHC. To ensure successful use of the ITk capabilities in Run 4 and beyond, the ATLAS tracking software has been successfully adapted to achieve state-of-the-art track reconstruction in challenging high-luminosity conditions with the ITk detector. This paper presents the expected tracking performance of the ATLAS ITk based on the latest available developments since the ITk technical design reports
    Archivio istituzionale della ricerca - Università di Trieste

    Performance of the upgraded PreProcessor of the ATLAS Level-1 Calorimeter Trigger

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    The PreProcessor of the ATLAS Level-1 Calorimeter Trigger prepares the analogue trigger signals sent from the ATLAS calorimeters by digitising, synchronising, and calibrating them to reconstruct transverse energy deposits, which are then used in further processing to identify event features. During the first long shutdown of the LHC from 2013 to 2014, the central components of the PreProcessor, the Multichip Modules, were replaced by upgraded versions that feature modern ADC and FPGA technology to ensure optimal performance in the high pile-up environment of LHC Run 2. This paper describes the features of the new Multichip Modules along with the improvements to the signal processing achieved
    Archivio della ricerca- Università di Roma La Sapienza

    Measurements of the suppression and correlations of dijets in Pb+Pb collisions at√sNN = 5.02 TeV

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    Studies of the correlations of the two highest transverse momentum (leading) jets in individual Pb+Pb collision events can provide information about the mechanism of jet quenching by the hot and dense matter created in such collisions. In Pb+Pb and pp collisions at√sNN = 5.02 TeV, measurements of the leading dijet transverse momentum (pT) correlations are presented. Additionally, measurements in Pb+Pb collisions of the dijet pair nuclear modification factors projected along leading and subleading jet pT are made. The measurements are performed using the ATLAS detector at the LHC with 260 pb−1 of pp data collected in 2017 and 2.2 nb−1 of Pb+Pb data collected in 2015 and 2018. An unfolding procedure is applied to the two-dimensional leading and subleading jet pT distributions to account for experimental effects in the measurement of both jets. Results are provided for dijets with leading jet pT greater than 100 GeV. Measurements of the dijet-yield-normalized xJ distributions in Pb+Pb collisions show an increased fraction of imbalanced jets compared to pp collisions; these measurements are in agreement with previous measurements of the same quantity at 2.76 TeV in the overlapping kinematic range. Measurements of the absolutely normalized dijet rate in Pb+Pb and pp collisions are also presented, and show that balanced dijets are significantly more suppressed than imbalanced dijets in Pb+Pb collisions. It is observed in the measurements of the pair nuclear modification factors that the subleading jets are significantly suppressed relative to leading jets with pT between 100 and 316 GeV for all centralities in Pb+Pb collisions
    Archivio della Ricerca - Università degli Studi di Siena
    Archivio istituzionale della ricerca - Università degli Studi di Udine

    Measurement of muon pairs produced via γγ scattering in nonultraperipheral Pb + Pb collisions at √sNN = 5.02 TeV with the ATLAS detector

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    Results of a measurement of dimuon photoproduction in nonultraperipheral Pb + Pb collisions at √sNN = 5.02 TeV are presented. Themeasurement uses ATLAS data from the 2015 and 2018 Pb + Pb data-taking periods at the LHC with an integrated luminosity of 1.94 nb.1. The γγ → μ+ μ- pairs are identified via selections on pair momentum asymmetry and acoplanarity. Differential cross sections for dimuon production are measured in different centrality, average muon momentum, and pair rapidity intervals as functions of acoplanarity and k⊥, the transverse momentum kick of one muon relative to the other. Measurements are also made as a function of the rapidity separation of the muons and the angle of the muon pair relative to the second-order event plane to test whether magnetic fields generated in the quark-gluon plasma affect the measured muons. A prior observation of a centrality-dependent broadening of the acoplanarity distribution is confirmed. Furthermore, the improved precision of the measurement reveals a depletion in the number of pairs having small acoplanarity or k⊥ values in more central collisions. The acoplanarity distributions in a given centrality interval are observed to vary with the mean pT of the muons in the pair, but the k⊥ distributions do not. Comparisons with recent theoretical predictions are made. The predicted trends associated with effects of magnetic fields on the dimuons are not observed
    Archivio della Ricerca - Università degli Studi di Siena
    Archivio istituzionale della ricerca - Università degli Studi di Udine

    Measurement of the tt ̄ cross section and its ratio to the Z production cross section using pp collisions at s=13.6 TeV with the ATLAS detector

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    The inclusive top-quark-pair production cross section σtt ̄ and its ratio to the Z-boson production cross section have been measured in proton–proton collisions at s=13.6 TeV, using 29 fb−1 of data collected in 2022 with the ATLAS experiment at the Large Hadron Collider. Using events with an opposite-charge electron-muon pair and b-tagged jets, and assuming Standard Model decays, the top-quark-pair production cross section is measured to be σtt ̄=850±3(stat.)±18(syst.)±20(lumi.) pb. The ratio of the tt ̄ and the Z-boson production cross sections is also measured, where the Z-boson contribution is determined for inclusive e+e− and μ+μ− events in a fiducial phase space. The relative uncertainty on the ratio is reduced compared to the tt ̄ cross section, thanks to the cancellation of several systematic uncertainties. The result for the ratio, Rtt ̄/Z=1.145±0.003(stat.)±0.021(syst.)±0.002(lumi.) is consistent with the Standard Model prediction using the PDF4LHC21 PDF set
    Archivio della Ricerca - Università degli Studi di Siena
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