Top Quark Asymmetries

Abstract

The production of top quark pairs (t$\overline{t}$) via the quark-antiquark initial state is not symmetric under the exchange of top quark and antiquark. Calculations of this next-to-leading order effect predict asymmetries of about one to a few percent, depending on the centre-of-mass energy and the selected phase space. Experimentally, this charge asymmetry of t$\overline{t}$ production manifests itself in differences in angular distributions between top quarks and antiquarks. Sensitive observables are the rapidities of the produced top quarks and antiquarks as well as their energies. In dileptonic t$\overline{t}$ events, the asymmetry of the t$\overline{t}$ system is reflected in a similar asymmetry in the system of the produced lepton pair, with the crucial advantage of a simpler reconstruction procedure. In this article we review the measurements of this effect in different final states and using different observables by the ATLAS and CMS Collaborations in LHC collisions at three different centre-of-mass energies