Measurement of the charge asymmetry in dileptonic decays of top quark pairs in $pp$ collisions at $\sqrt{s}=7$ TeV using the ATLAS detector

A measurement of the top-antitop ($t\bar{t}$) charge asymmetry is presented using data corresponding to an integrated luminosity of 4.6 fb${}^{-1}$ of LHC $pp$ collisions at a centre-of-mass energy of 7 TeV collected by the ATLAS detector. Events with two charged leptons, at least two jets and large missing transverse momentum are selected. Two observables are studied: $A_{\text{C}}^{\mathrm{\ell }\mathrm{\ell }}$ based on the identified charged leptons, and $A_{\text{C}}^{t\bar{t}}$, based on the reconstructed $t\bar{t}$ final state. The asymmetries are measured to be \begin{eqnarray*} A^{\ell\ell}{$\text{C}$} & = & 0.024 \pm 0.015 ~$\text{(stat.)}$ \pm 0.009 ~$\text{(syst.)}$, \end{eqnarray*} \begin{eqnarray*} A^{t\bar{t}}{$\text{C}$} & = & 0.021 \pm 0.025 ~$\text{(stat.)}$ \pm 0.017 ~$\text{(syst.)}$. \end{eqnarray*} The measured values are in agreement with the Standard Model predictions.