Measurements of normalized differential cross-sections for ttbar production in pp collisions at sqrt(s) = 7 TeV using the ATLAS detector

TL;DR

This paper reports measurements of normalized differential cross-sections for top-quark pair production at 7 TeV, comparing data with simulations and theory, revealing generally good agreement but some discrepancies at high kinematic values.

Contribution

It provides the first detailed measurements of differential cross-sections for ttbar production at 7 TeV, aiding validation of theoretical models and parton distribution functions.

Findings

Data are in fair agreement with predictions across a wide range.

Distributions are softer than predictions at high ttbar mass and top-quark pT.

Results help discriminate among different parton distribution functions.

Abstract

Measurements of normalized differential cross-sections for top-quark pair production are presented as a function of the top-quark transverse momentum, and of the mass, transverse momentum, and rapidity of the ttbar system, in proton--proton collisions at a center-of-mass energy of sqrt(s) = 7 TeV. The dataset corresponds to an integrated luminosity of 4.6 fb^-1, recorded in 2011 with the ATLAS detector at the CERN Large Hadron Collider. Events are selected in the lepton+jets channel, requiring exactly one lepton and at least four jets with at least one of the jets tagged as originating from a b-quark. The measured spectra are corrected for detector efficiency and resolution effects and are compared to several Monte Carlo simulations and theory calculations. The results are in fair agreement with the predictions in a wide kinematic range. Nevertheless, data distributions are softer than predicted for higher values of the mass of the ttbar system and of the top-quark transverse momentum. The measurements can also discriminate among different sets of parton distribution functions.