Measurement of the charge asymmetry in top quark pair production in pp collisions at sqrt{s}=7 TeV using the ATLAS detector

A measurement of the top-antitop charge asymmetry is presented using data corresponding to an integrated luminosity of 0.70${\rm fb}^{-1}$ of $pp$ collisions at $\sqrt{s} = 7$ TeV collected by the ATLAS detector. Selected events are required to have a single lepton (electron or muon), large missing transverse energy and at least four jets. A kinematic likelihood is used to reconstruct the $t\bar{t}$ event topology. After background subtraction, a Bayesian unfolding procedure is performed to correct for acceptance and detector effects. The charge asymmetry observable $A_C$ is defined as: \begin{equation} A_C = \frac{N(\Delta |Y| >0) - N(\Delta |Y| <0)}{N(\Delta |Y| >0) + N(\Delta |Y| <0)}, \nonumber \end{equation} where $\Delta |Y|$ represents the difference of the absolute values of top and antitop rapidities, $\Delta |Y| = |Y_t| - |Y_{\bar{t}}|$. The charge asymmetry is measured to be: \begin{eqnarray*} A_{\textrm{C}} = -0.009 \pm 0.023\,\rm{(stat.)} \pm 0.032\,\rm{(syst.)} \quad \text{(e+jets channel)} \\ A_{\textrm{C}} = -0.028 \pm 0.019\,\rm{(stat.)} \pm 0.022\,\rm{(syst.)} \quad \text{($\mu$+jets channel)} \end{eqnarray*} giving a combined value of: \begin{eqnarray*} A_{\textrm{C}} & = & -0.024 \pm 0.016 \ \text{(stat)} \pm \rm{0.023} \ \text{(syst)}, \end{eqnarray*} in agreement with the Standard Model prediction: $A_{\textrm{C}} = 0.006.$