Differential top–antitop production cross-section measurements in pp collisions at $\sqrt{s} = 7$ TeV as a function of pseudo-top-quark observables in the single-lepton channel using the ATLAS detector

The differential top-quark pair production cross-section is presented in terms of a top-quark proxy observable referred to as the pseudo-top-quark whose dependence on theoretical models is minimal. The pseudo-top-quark observable is defined both in terms of reconstructed objects and stable particles. The measurements are performed on $t\bar{t}$ events in the lepton+jets channel, requiring exactly one lepton and at least four jets with at least two of them $b$-tagged. The measurements are performed for hadronic and leptonic pseudo-top-quarks, defined by the $W$ boson decays, in the single lepton channel and as a combination of lepton channels. The dataset corresponds to an integrated luminosity of 4.6~fb$^{-1}$ of proton-proton collisions at $\sqrt{s} = 7$ TeV collected by the ATLAS detector at the LHC. The production cross-section is measured as a function of the transverse momentum and rapidity of the hadronic or leptonic pseudo-top-quark as well as the transverse momentum, rapidity and invariant mass of the pseudo-top-quark pair system. The measurements are shown after corrections for detector effects and are presented within a kinematic range that closely matches the detector acceptance. Differential cross-section measurements of the pseudo-top-quark variables are compared with several current Monte Carlo models that implement next-to-leading order or leading order multi-leg matrix element calculations.