1,733,724 research outputs found
Erratum: Precision measurement of the B 0 meson lifetime using B 0 → J / ψ K ∗ 0 decays with the ATLAS detector
No full textErratum to: Observation of four-top-quark production in the multilepton final state with the ATLAS detector
No full textSearch for top-philic heavy resonances in pp collisions at with the ATLAS detector
No full textA search for the associated production of a heavy resonance with a top-quark or a top-antitop-quark pair, and decaying into a pair is presented. The search uses the data recorded by the ATLAS detector in pp collisions at at the Large Hadron Collider during the years 2015–2018, corresponding to an integrated luminosity of 139 . Events containing exactly one electron or muon are selected. The two hadronically decaying top quarks from the resonance decay are reconstructed using jets clustered with a large radius parameter of . The invariant mass spectrum of the two top quark candidates is used to search for a resonance signal in the range of 1.0 to 3.2 . The presence of a signal is examined using an approach with minimal model dependence followed by a model-dependent interpretation. No significant excess is observed over the background expectation. Upper limits on the production cross section times branching ratio at 95% confidence level are provided for a heavy boson based on a simplified model, for mass between 1.0 and 3.0 . The observed (expected) limits range from 21 (14) fb to 119 (86) fb depending on the choice of model parameters
Measurement of the Lund jet plane in hadronic decays of top quarks and W bosons with the ATLAS detector
No full textAbstract The Lund jet plane (LJP) is measured for the first time in t t ¯ events, using 140 fb - 1 of s = 13 TeV pp collision data collected with the ATLAS detector at the LHC. The LJP is a two-dimensional observable of the sub-structure of hadronic jets that acts as a proxy for the kinematics of parton showers and hadron formation. The observable is constructed from charged particles and is measured for R = 1.0 anti- k t jets with transverse momentum above 350 GeV containing the full decay products of either a top quark or a daughter W boson. The other top quark in the event is identified from its decay into a b-quark, an electron or a muon and a neutrino. The measurement is corrected for detector effects and compared with a range of Monte Carlo predictions sensitive to different aspects of the hadronic decays of the heavy particles. In the W-boson-initiated jets, all the predictions are incompatible with the measurement. In the top quark initiated jets, disagreement with all predictions is observed in smaller subregions of the plane, and with a subset of the predictions across the fiducial plane. The measurement could be used to improve the tuning of Monte Carlo generators, for better modelling of hadronic decays of heavy quarks and bosons, or to improve the performance of jet taggers
Measurements of Higgs boson production via gluon–gluon fusion and vector-boson fusion using H → W W ∗ → ℓ ν ℓ ν decays in pp collisions with the ATLAS detector and their effective field theory interpretations
No full textAbstract Higgs boson production cross-sections via gluon–gluon fusion and vector-boson fusion in proton–proton collisions are measured in the H → W W ∗ → ℓ ν ℓ ν decay channel. The Large Hadron Collider delivered proton–proton collisions at a centre-of-mass energy of 13 TeV between 2015 and 2018, which were recorded by the ATLAS detector, corresponding to an integrated luminosity of 140 fb - 1 . The total cross-sections for Higgs boson production by gluon–gluon fusion and vector-boson fusion times the H → W W ∗ branching ratio are measured to be 12 . 4 - 1.2 + 1.3 pb and 0 . 79 - 0.16 + 0.18 pb , respectively, in agreement with the Standard Model predictions. Higgs boson production is further characterised through measurements of Simplified Template Cross-Sections in a total of fifteen kinematic fiducial regions. A new scheme of kinematic fiducial regions has been introduced to enhance the sensitivity to CP-violating effects in Higgs boson interactions. Both schemes are used to constrain CP-even and CP-odd dimension-six operators in the Standard Model effective field theor
The environmental impact, carbon emissions and sustainability of computing in the ATLAS experiment
No full textAbstract ATLAS, a general-purpose experiment at the Large Hadron Collider (LHC), makes use of a large internationally-distributed computing infrastructure, including over 10 6 TB of managed data on disk and tape and almost one million simultaneously running CPU cores. Upgrades for the High-Luminosity LHC (HL-LHC) will increase the required computing resources by a factor of 3–4 by the beginning of the 2030s, and by an order of magnitude before the conclusion of data taking at the beginning of the 2040s. These resources are spread over around 100 computing sites worldwide. Efforts are underway within the experiment to evaluate and mitigate various aspects of the environmental impact of the sites, with the additional long-term goal of making recommendations to the sites that will significantly reduce the total expected environmental impact in the HL-LHC era. These efforts take several forms: building awareness in the experiment community, adjusting aspects of the computing policy, and modifications of data center configurations, either in ways that take advantage of particular features of ATLAS workloads or in generic ways that reduce the environmental impact of the computing resources. This paper describes the ongoing investigations and approaches that have already provided useful and actionable outcomes
Measurement of hard double-parton interactions in W(→ lν) + 2-jet events at √s = 7 TeV with the ATLAS detector
No full textMeasurement of W ± -boson differential cross-sections in proton–proton collisions with low pile-up data at s = 5.02 TeV and 13 TeV with the ATLAS detector
No full textAbstract High precision single-differential W ± -boson production cross-sections as a function of electron or muon transverse momentum p T or their pseudorapity η , as well as double-differential cross-sections as functions of these variables, are measured in proton–proton collisions at centre-of-mass energies s = 5.02 TeV and 13 TeV. The W-boson charge asymmetry as a function of lepton η is also measured. The data, collected in dedicated runs at reduced instantaneous luminosity with the ATLAS detector at the Large Hadron Collider, correspond to integrated luminosities of 255 pb - 1 at 5.02 TeV and 338 pb - 1 at 13 TeV. The measurements are in agreement with Standard-Model predictions calculated at next-to-next-to-leading-order in the strong coupling constant α s including transverse-momentum resummation at next-to-next-to-leading logarithmic accuracy using several parton distribution functions. The impact of the measured differential cross-sections as a function of lepton η on the determination of these functions is studied using a profiling technique
Energy scale and resolution for anti- k t jets with radius parameters R = 0.2 and 0.6 measured in proton-proton collisions at s = 13 TeV with the ATLAS detector
No full textJets with different radius parameters R are an important tool for probing quantum chromodynamics processes at different angular scales. Jets with small R = 0.2 are instrumental in measurements of the substructure of large-R jets resulting from collimated hadronic decays of energetic W, Z, and Higgs bosons, top quarks, and of potential new resonances. This paper presents measurements of the energy scale, resolution, and associated uncertainties of jets with radius parameters R = 0.2 and 0.6, obtained using the ATLAS detector. The results are based on 37 fb - 1 of proton–proton collision data from the Large Hadron Collider at a centre-of-mass energy of s = 13 TeV. A new in situ method for measuring jet energy scale differences between data and Monte Carlo simulations is presented. The systematic uncertainties in the jet energy scale for central jets ( | η | < 1.2 ) typically vary from 1% to about 5% as a function of | η | at very low transverse momentum, p T , of around 20 GeV for both R = 0.2 and 0.6 jets. The relative energy resolution ranges from ( 35 ± 6 ) % at p T = 20 GeV to ( 6 ± 0.5 ) % at p T = 300 GeV for central R = 0.2 jets, and is found to be slightly worse for R = 0.6 jets. Finally, the effect of close-by hadronic activity on the jet energy scale is investigated and is found to be well modelled by the ATLAS Monte Carlo simulations
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