  A measurement of the charge asymmetry in the production of top quark pairs in
the semileptonic decay channel has been performed. A dataset corresponding to
an integrated luminosity of 1.04 inverse femtobarn, obtained at a
centre-of-mass energy of 7 TeV with the ATLAS experiment at the LHC, was used.
After performing a selection of events with one isolated lepton, at least four
jets and missing transverse energy, a kinematic fit was performed to
reconstruct the top-antitop event topology. The charge asymmetry was determined
using the differential distribution of the difference of absolute reconstructed
rapidities of the top and antitop quark. An unfolding procedure was applied to
correct for detector acceptance and resolution effects and to obtain the
corresponding distribution at parton level. The total charge asymmetry after
unfolding was measured to be A_C = -0.018 +/- 0.028 (stat.) +/- 0.023 (syst.)
in agreement with the Standard Model prediction. In addition, a simultaneous
unfolding in the difference of absolute reconstructed rapidities of the top and
antitop quark and the invariant mass of the top-antitop pair was performed.
