It has been found that the theoretical predictions for W and Z boson cross sections, and for the W boson charge asymmetry, which are labelled as NNPDF3.1 1 have in fact been calculated using the ...NNPDF3.0 PDF set 2 instead.
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The performance of identification algorithms ("taggers") for hadronically decaying top quarks and W bosons in pp collisions at Formula omitted = 13 TeV recorded by the ATLAS experiment at the Large ...Hadron Collider is presented. A set of techniques based on jet shape observables are studied to determine a set of optimal cut-based taggers for use in physics analyses. The studies are extended to assess the utility of combinations of substructure observables as a multivariate tagger using boosted decision trees or deep neural networks in comparison with taggers based on two-variable combinations. In addition, for highly boosted top-quark tagging, a deep neural network based on jet constituent inputs as well as a re-optimisation of the shower deconstruction technique is presented. The performance of these taggers is studied in data collected during 2015 and 2016 corresponding to 36.1 fb Formula omitted for the Formula omitted and Formula omitted and 36.7 fb Formula omitted for the dijet event topologies.
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The production cross-sections for Formula omitted and Z bosons are measured using ATLAS data corresponding to an integrated luminosity of 4.0 pb Formula omitted collected at a centre-of-mass energy ...Formula omitted TeV. The decay channels Formula omitted and Formula omitted are used, where Formula omitted can be an electron or a muon. The cross-sections are presented for a fiducial region defined by the detector acceptance and are also extrapolated to the full phase space for the total inclusive production cross-section. The combined (average) total inclusive cross-sections for the electron and muon channels are: sigmaW+right arrowlνtot=2312±26(stat.)±27(syst.)±72(lumi.)±30(extr.)pb,sigmaW-right arrowlνtot=1399±21(stat.)±17(syst.)±43(lumi.)±21(extr.)pb,sigmaZright arrowlltot=323.4±9.8(stat.)±5.0(syst.)±10.0(lumi.)±5.5(extr.)pb.Measured ratios and asymmetries constructed using these cross-sections are also presented. These observables benefit from full or partial cancellation of many systematic uncertainties that are correlated between the different measurements.
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The top quark mass is measured using a template method in the Formula omitted channel (lepton is e or Formula omitted) using ATLAS data recorded in 2012 at the LHC. The data were taken at a ...proton-proton centre-of-mass energy of Formula omitted Formula omitted and correspond to an integrated luminosity of Formula omitted fb Formula omitted. The Formula omitted channel is characterized by the presence of a charged lepton, a neutrino and four jets, two of which originate from bottom quarks (b). Exploiting a three-dimensional template technique, the top quark mass is determined together with a global jet energy scale factor and a relative b-to-light-jet energy scale factor. The mass of the top quark is measured to be Formula omitted Formula omitted. A combination with previous ATLAS Formula omitted measurements gives Formula omitted Formula omitted.
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This paper describes a study of techniques for identifying Higgs bosons at high transverse momenta decaying into bottom-quark pairs, Formula omitted, for proton-proton collision data collected by the ...ATLAS detector at the Large Hadron Collider at a centre-of-mass energy Formula omitted Formula omitted. These decays are reconstructed from calorimeter jets found with the anti- Formula omitted Formula omitted jet algorithm. To tag Higgs bosons, a combination of requirements is used: b-tagging of Formula omitted track-jets matched to the large-R calorimeter jet, and requirements on the jet mass and other jet substructure variables. The Higgs boson tagging efficiency and corresponding multijet and hadronic top-quark background rejections are evaluated using Monte Carlo simulation. Several benchmark tagging selections are defined for different signal efficiency targets. The modelling of the relevant input distributions used to tag Higgs bosons is studied in 36 fb Formula omitted of data collected in 2015 and 2016 using Formula omitted and Formula omitted event selections in data. Both processes are found to be well modelled within the statistical and systematic uncertainties.
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This paper presents measurements of \W^{\pm }Z\ production cross sections in pp collisions at a centre-of-mass energy of 13 \\text {TeV}\. The data were collected in 2015 and 2016 by the ATLAS ...experiment at the Large Hadron Collider, and correspond to an integrated luminosity of \36.1~\hbox {fb}^{-1}\. The \W^{\pm }Z\ candidate events are reconstructed using leptonic decay modes of the gauge bosons into electrons and muons. The measured inclusive cross section in the detector fiducial region for a single leptonic decay mode is \\sigma _{W^\pm Z \rightarrow \ell ^{'} \nu \ell \ell }^{\text {fid.}} = 63.7 \, \pm ~1.0~\text {(stat.)} \, \pm ~2.3~\text {(syst.)} \, \pm ~1.4~\text {(lumi.)}\ fb, reproduced by the next-to-next-to-leading-order Standard Model prediction of \61.5^{+1.4}_{-1.3}\ fb. Cross sections for \W^+Z\ and \W^-Z\ production and their ratio are presented as well as differential cross sections for several kinematic observables. An analysis of angular distributions of leptons from decays of W and Z bosons is performed for the first time in pair-produced events in hadronic collisions, and integrated helicity fractions in the detector fiducial region are measured for the W and Z bosons separately. Of particular interest, the longitudinal helicity fraction of pair-produced vector bosons is also measured.
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Measurements of fiducial integrated and differential cross sections for inclusive Formula omitted, Formula omitted and Z boson production are reported. They are based on Formula omitted of pp ...collision data at Formula omitted TeV collected with the ATLAS detector at the CERN Large Hadron Collider. Electron and muon decay channels are analysed, and the combined Formula omitted, Formula omitted and Z integrated cross sections are found to be Formula omitted pb, Formula omitted pb, and Formula omitted pb, in good agreement with next-to-next-to-leading-order QCD cross-section calculations. These measurements serve as references for Pb+Pb interactions at the LHC at Formula omitted TeV.
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This paper presents measurements of charged-particle distributions sensitive to the properties of the underlying event in events containing a Formula omitted boson decaying into a muon pair. The data ...were obtained using the ATLAS detector at the LHC in proton-proton collisions at a centre-of-mass energy of 13 Formula omitted with an integrated luminosity of Formula omitted. Distributions of the charged-particle multiplicity and of the charged-particle transverse momentum are measured in regions of the azimuth defined relative to the Formula omitted boson direction. The measured distributions are compared with the predictions of various Monte Carlo generators which implement different underyling event models. The Monte Carlo model predictions qualitatively describe the data well, but with some significant discrepancies.
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Previous studies have shown that weighted angular moments derived from jet constituents encode the colour connections between partons that seed the jets. This paper presents measurements of two such ...distributions, the jet-pull angle and jet-pull magnitude, both of which are derived from the jet-pull angular moment. The measurement is performed in Formula omitted events with one leptonically decaying W boson and one hadronically decaying W boson, using Formula omitted of pp collision data recorded by the ATLAS detector at Formula omitted delivered by the Large Hadron Collider. The observables are measured for two dijet systems, corresponding to the colour-connected daughters of the W boson and the two b-jets from the top-quark decays, which are not expected to be colour connected. To allow the comparison of the measured distributions to colour model predictions, the measured distributions are unfolded to particle level, after correcting for experimental effects introduced by the detector. While good agreement can be found for some combinations of predictions and observables, none of the predictions describes the data well across all observables.
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Measurements of the azimuthal anisotropy in lead-lead collisions at Formula omitted = 5.02 TeV are presented using a data sample corresponding to 0.49 Formula omitted integrated luminosity collected ...by the ATLAS experiment at the LHC in 2015. The recorded minimum-bias sample is enhanced by triggers for "ultra-central" collisions, providing an opportunity to perform detailed study of flow harmonics in the regime where the initial state is dominated by fluctuations. The anisotropy of the charged-particle azimuthal angle distributions is characterized by the Fourier coefficients, Formula omitted- Formula omitted, which are measured using the two-particle correlation, scalar-product and event-plane methods. The goal of the paper is to provide measurements of the differential as well as integrated flow harmonics Formula omitted over wide ranges of the transverse momentum, 0.5 Formula omitted 60 GeV, the pseudorapidity, Formula omitted 2.5, and the collision centrality 0-80%. Results from different methods are compared and discussed in the context of previous and recent measurements in Pb+Pb collisions at Formula omitted = 2.76 Formula omitted and 5.02 Formula omitted. In particular, the shape of the Formula omitteddependence of elliptic or triangular flow harmonics is observed to be very similar at different centralities after scaling the Formula omitted and Formula omittedvalues by constant factors over the centrality interval 0-60% and the Formula omittedrange 0.5 Formula omitted 5 GeV.
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