193 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 reconstruction of the signal from hadrons and jets emerging from the proton–proton collisions at the Large Hadron Collider (LHC) and entering the ATLAS calorimeters is based on a three-dimensional topological clustering of individual calorimeter cell signals. The cluster formation follows cell signal-significance patterns generated by electromagnetic and hadronic showers. In this, the clustering algorithm implicitly performs a topological noise suppression by removing cells with insignificant signals which are not in close proximity to cells with significant signals. The resulting topological cell clusters have shape and location information, which is exploited to apply a local energy calibration and corrections dependingmore » on the nature of the cluster. Lastly, topological cell clustering is established as a well-performing calorimeter signal definition for jet and missing transverse momentum reconstruction in ATLAS.« less

In the original paper, Fig. 4 contains the wrong label preliminary. The label has been fixed, while none of the results have changed.

This paper presents the method and performance of primary vertex reconstruction in proton–proton collision data recorded by the ATLAS experiment during Run 1 of the LHC. The studies presented focus on data taken during 2012 at a centre-of-mass energy of √s = 8 TeV. The performance has been measured as a function of the number of interactions per bunch crossing over a wide range, from one to seventy. The measurement of the position and size of the luminous region and its use as a constraint to improve the primary vertex resolution are discussed. A longitudinal vertex position resolution of aboutmore » 30 μm is achieved for events with high multiplicity of reconstructed tracks. The transverse position resolution is better than 20 μm and is dominated by the precision on the size of the luminous region. An analytical model is proposed to describe the primary vertex reconstruction efficiency as a function of the number of interactions per bunch crossing and of the longitudinal size of the luminous region. Agreement between the data and the predictions of this model is better than 3% up to seventy interactions per bunch crossing.« less

The reconstruction and calibration algorithms used to calculate missing transverse momentum (E^miss_T) with the ATLAS detector exploit energy deposits in the calorimeter and tracks reconstructed in the inner detector as well as the muon spectrometer. Various strategies are used to suppress effects arising from additional proton–proton interactions, called pileup, concurrent with the hard-scatter processes. Tracking information is used to distinguish contributions from the pileup interactions using their vertex separation along the beam axis. The performance of the E^miss_T reconstruction algorithms, especially with respect to the amount of pileup, is evaluated using data collected in proton–proton collisions at a centre-of-mass energymore » of 8 TeV during 2012, and results are shown for a data sample corresponding to an integrated luminosity of 20.3fb^–1. The simulation and modelling of E^miss_T in events containing a Z boson decaying to two charged leptons (electrons or muons) or a W boson decaying to a charged lepton and a neutrino are compared to data. The acceptance for different event topologies, with and without high transverse momentum neutrinos, is shown for a range of threshold criteria for E^miss_T, and estimates of the systematic uncertainties in the E^miss_T measurements are presented.« less

Direct searches for lepton flavour violation in decays of the Higgs and Z bosons with the ATLAS detector at the LHC are presented. The following three decays are considered: H → eτ, H → μτ, and Z → μτ. The searches are based on the data sample of proton–proton collisions collected by the ATLAS detector corresponding to an integrated luminosity of 20.3 fb^–1 at a centre-of-mass energy of √s = 8 TeV. No significant excess is observed, and upper limits on the lepton-flavour-violating branching ratios are set at the 95% confidence level: Br(H → eτ) < 1.04%, Br(H → μτ)more » < 1.43%, and Br(Z → μτ) < 1.69 × 10^–5.« less