Differential top-antitop cross-section measurements as a function of observables constructed from final-state particles using pp collisions at $\sqrt{s}=7$ TeV in the ATLAS detector

TL;DR

This paper reports measurements of differential top-antitop quark pair production cross-sections as functions of various kinematic variables, using 7 TeV proton-proton collision data from the ATLAS detector, with minimal model dependence.

Contribution

It presents novel differential cross-section measurements based on the pseudo-top-quark in lepton+jets events, comparing results with multiple Monte Carlo models.

Findings

Differential cross-sections are measured with high precision.

Results show minimal dependence on theoretical models.

Data agree well with several Monte Carlo predictions.

Abstract

Various differential cross-sections are measured in top-quark pair ($t\bar{t}$) events produced in proton-proton collisions at a centre-of-mass energy of $\sqrt{s} = 7$ TeV at the LHC with the ATLAS detector. These differential cross-sections are presented in a data set corresponding to an integrated luminosity of $4.6$ fb$^{-1}$. The differential cross-sections are presented in terms of kinematic variables, such as momentum, rapidity and invariant mass, of a top-quark proxyreferred to as the pseudo-top-quark as well as the pseudo-top-quark pair system. The dependence of the measurement on theoretical models is minimal. The measurements are performed on $t\bar{t}$ events in the lepton+jets channel, requiring exactly one charged lepton and at least four jets with at least two of them tagged as originating from a $b$-quark. The hadronic and leptonic pseudo-top-quarks are defined via the leptonic or hadronic decay mode of the $W$ boson produced by the top-quark decay in events with a single charged lepton. Differential cross-section measurements of the pseudo-top-quark variables are compared with several Monte Carlo models that implement next-to-leading order or leading-order multi-leg matrix-element calculations.