Measurement of single top-quark production in association with a W boson in the single-lepton channel at $\sqrt{s} = 8\,\text {TeV}$ with the ATLAS detector

Abstract The production cross-section of a top quark in association with a W boson is measured using proton–proton collisions at $\sqrt{s} = 8\,\text {TeV}$ s = 8 TeV . The dataset corresponds to an integrated luminosity of $20.2\,\text {fb}^{-1}$ 20.2 fb - 1 , and was collected in 2012 by the ATLAS detector at the Large Hadron Collider at CERN. The analysis is performed in the single-lepton channel. Events are selected by requiring one isolated lepton (electron or muon) and at least three jets. A neural network is trained to separate the tW signal from the dominant $t{\bar{t}}$ t t ¯ background. The cross-section is extracted from a binned profile maximum-likelihood fit to a two-dimensional discriminant built from the neural-network output and the invariant mass of the hadronically decaying W boson. The measured cross-section is $\sigma _{tW} = 26 \pm 7\,\text {pb}$ σ tW = 26 ± 7 pb , in good agreement with the Standard Model expectation.