Measurements of the charge asymmetry in top-quark pair production in the dilepton final state at $\sqrt{s}=8$ TeV with the ATLAS detector

TL;DR

This paper measures the charge asymmetry in top-quark pair production in dilepton final states at 8 TeV using ATLAS data, comparing results with Standard Model predictions.

Contribution

It provides the first detailed measurements of charge asymmetry in top-quark pairs in dilepton channels at 8 TeV, including differential analyses and comparison with theoretical expectations.

Findings

Measured asymmetries are consistent with Standard Model predictions.

Inclusive asymmetries are close to zero within uncertainties.

Differential asymmetries as functions of kinematic variables are also reported.

Abstract

Measurements of the top--antitop quark pair production charge asymmetry in the dilepton channel, characterized by two high-${p}_{\rm{T}}$ leptons (electrons or muons), are presented using data corresponding to an integrated luminosity of $20.3$ $\textrm{fb}^{-1}$ from $pp$ collisions at a center-of-mass energy of $\sqrt{s} = 8$ TeV collected with the ATLAS detector at the Large Hadron Collider at CERN. Inclusive and differential measurements as a function of the invariant mass, transverse momentum, and longitudinal boost of the $t\bar{t}$ system are performed both in the full phase space and in a fiducial phase space closely matching the detector acceptance. Two observables are studied: $A^{\ell\ell}_{\textrm{C}}$ based on the selected leptons and $A^{t\bar{t}}_{\textrm{C}}$ based on the reconstructed $t\bar{t}$ final state. The inclusive asymmetries are measured in the full phase space to be $A^{\ell\ell}_{\textrm{C}} = 0.008 \pm 0.006$ and $A^{t\bar{t}}_{\textrm{C}} = 0.021 \pm 0.016$, which are in agreement with the Standard Model predictions of $A^{\ell\ell}_{\textrm{C}} = 0.0064 \pm 0.0003 $ and $A^{t\bar{t}}_{\textrm{C}} = 0.0111 \pm 0.0004$.