710 Search Results

One correction is noted for the paper. The branching fraction ($$\mathcal{B}$$($$W →{ℓv}$$) = 0.3246 was not included in the conversion of the observed cross-section limit, σ x $$\mathcal{B}$$( $t →Wb$) x ($$\mathcal{B}$$($$W →{ℓv}$$) < 2.9to the coupling constants $$κ_{ugt}$$ and $$κ_{cgt}$$ and the branching fractions $$\mathcal{B}$$( $t →ug$) and $$\mathcal{B}$$( $t →cg$). The inclusion leads to weaker observed exclusion limits on the coupling constants divided by the scale of new physics of $$k_{ugt}$$/ Λ <10 x 10^-3 TeV^-1 and $$k_{cgt}$$/Λ <23 x 10^-3 TeV^-1 and on the branching fractions $$\mathcal{B}$$( $t →ug$) < 1.2 x10^-4 and $$\mathcal{B}$$( $t →cg$) <more » 6.4 x 10^-4. The predicted exclusion limits on the coupling constants divided by the scale of new physics are $$k_{ugt}$$/ Λ < 9.5 x 10^-3 TeV^-1and $$\mathcal{B}$$( $t →cg$)/ Λ < 22 x 10^-3 TeV^-1 and on the branching fractions $$\mathcal{B}$$( $t →ug$) < 1.1 x 10^-4 and $$\mathcal{B}$$( $t →cg$) < 5.7 x 10^-4. Updated distributions of the observed upper limits on the coupling constants for combinations of cgt and ugt channels are shown in Figure 10a and on the branching fractions in Figure 10b.« less

The jet energy scale, jet energy resolution, and their systematic uncertainties are measured for jets reconstructed with the ATLAS detector in 2012 using proton–proton data produced at a centre-of-mass energy of 8 TeV with an integrated luminosity of 20fb^-1. Jets are reconstructed from clusters of energy depositions in the ATLAS calorimeters using the anti-k_t algorithm. A jet calibration scheme is applied in multiple steps, each addressing specific effects including mitigation of contributions from additional proton–proton collisions, loss of energy in dead material, calorimeter non-compensation, angular biases and other global jet effects. The final calibration step uses several in situ techniquesmore » and corrects for residual effects not captured by the initial calibration. Furthermore, these analyses measure both the jet energy scale and resolution by exploiting the transverse momentum balance in γ + jet, Z + jet, dijet, and multijet events. A statistical combination of these measurements is performed. In the central detector region, the derived calibration has a precision better than 1% for jets with transverse momentum 150 GeV < p_T < 1500 GeV, and the relative energy resolution is (8.4 ± 0.6)% for p_T=100 GeV and (23 ± 2)% for p_T=20 GeV. The calibration scheme for jets with radius parameter R = 1.0, for which jets receive a dedicated calibration of the jet mass, is also discussed.« less

Two additions impacting tables 3 and 4 in ref. [1] are presented in the following. No significant impact is found for other results or figures in ref. [1].

Searches for scalar leptoquarks pair-produced in proton–proton collisions at $$\sqrt{s}$$ =13 TeV at the Large Hadron Collider are performed by the ATLAS experiment. A data set corresponding to an integrated luminosity of 36.1 fb^-1 is used. Final states containing two electrons or two muons and two or more jets are studied, as are states with one electron or muon, missing transverse momentum and two or more jets. No statistically significant excess above the Standard Model expectation is observed. The observed and expected lower limits on the leptoquark mass at 95% confidence level extend up to 1.29 TeV and 1.23 TeV for first- and second-generationmore » leptoquarks, respectively, as postulated in the minimal Buchmüller–Rückl–Wyler model, assuming a branching ratio into a charged lepton and a quark of 50%. In addition, measurements of particle-level fiducial and differential cross sections are presented for the Z→ ee, Z→ μμ and $$ t\bar{t} $$ processes in several regions related to the search control regions. Predictions from a range of generators are compared with the measurements, and good agreement is seen for many of the observables. However, the predictions for the Z→ ℓℓ measurements in observables sensitive to jet energies disagree with the data.« less

One correction is made to the figure 4e of the paper. The reported cross-sections, both the experimental upper limits and the theoretical prediction, corresponded only to a fiducial region of the phase space with at least two prompt same-sign electrons or muons before detector simulation (p_T > 10 GeV, |η| < 2.8). The updated figure 4e instead presents the results without this requirement, i.e. in the full phase space as it should, given the y-axis label of the plot. The reported sensitivity of the analysis, i.e. the ability to exclude top squark masses below 700 GeV in this scenario, ismore » however unchanged since the same requirements were applied to the analysis and to the theory predictions.« less

This paper presents measurements of W^±Z production cross sections in pp collisions at a centre-of-mass energy of 13 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 fb^-1. The W^±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 σ$$fid.\atop{W^±Z→ℓ'νℓℓ}$$ = 63.7± 1.0 (stat.)± 2.3 (syst.)± 1.4 (lumi.) fb, reproduced by the next-to-next-to-leading-order Standard Model prediction of 61.5$$+1.4\atop{-1.3}$$ fb.more » 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.« less