Evidence for a mass dependent forward-backward asymmetry in top quark pair production

We present a new measurement of the inclusive forward-backward t (t) over bar production asymmetry and its rapidity and mass dependence. The measurements are performed with data corresponding to an integrated luminosity of 5.3 fb(-1) of p (p) over bar collisions at root s = 1.96 TeV, recorded with the CDF-II Detector at the Fermilab Tevatron. Significant inclusive asymmetries are observed in both the laboratory frame and the t (t) over bar rest frame, and in both cases are found to be consistent with CP conservation under interchange of t and (t) over bar. In the t (t) over bar rest frame, the asymmetry is observed to increase with the t (t) over bar rapidity difference, Delta y, and with the invariant mass M(t (t) over bar) of the t (t) over bar system. Fully corrected parton-level asymmetries are derived in two regions of each variable, and the asymmetry is found to be most significant at large Delta y and M(t (t) over bar). For M(t (t) over bar) >= 450 GeV/c(2), the parton-level asymmetry in the t (t) over bar rest frame is A(t (t) over bar) = 0.475 +/- 0.114 compared to a next-to-leading order QCD prediction of 0.088 +/- 0.013.