Measurement of the leptonic asymmetry in tt̄ events produced in pp̄ collisions at √s=1.96 TeV

We measure the asymmetry in the charge-weighted rapidity qy(l) of the lepton in semileptonic t (t) over bar decays recorded with the CDF II detector using the full Tevatron Run II sample, corresponding to an integrated luminosity of 9: 4 fb(-1). A parametrization of the asymmetry as a function of qy(l) is used to correct for the finite acceptance of the detector and recover the production-level asymmetry. The result of A(FB)(l) = 0.094(-0.029)(+0.032) is to be compared to the standard model next-to-leading-order prediction of A(FB)(l) = 0.038 +/- 0.003.