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.
Highlights
The large number of top-quark pair events produced at the Large Hadron Collider (LHC) has allowed the ATLAS [1] and CMS [2] experiments to perform precise inclusive and differential top-quark related cross-section measurements
This paper presents differential ttcross-section measurements using a definition where the variables are constructed from an object that is directly related to detectorlevel observables
The measurements can be directly compared to Monte Carlo simulations that are generated with top quarks with a mass of 172.5 GeV
Summary
The large number of top-quark pair (tt) events produced at the Large Hadron Collider (LHC) has allowed the ATLAS [1] and CMS [2] experiments to perform precise inclusive and differential top-quark related cross-section measurements Both experiments have recently published measurements of the inclus√ive ttproduction cross-section in proton-proton (pp) collisions at centre-of-mass energies, s, of 7 and 8 TeV [3,4,5,6,7,8,9,10,11,12,13,14] as well as differential crosssection measurements as functions of the top-quark transverse momentum (pT) and rapidity (y), and of the mass (mtt) and y of the ttsystem [15,16,17]. From these variations a normalisation uncertainty of 50% is assigned
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