Forward-Backward Asymmetry at High Mass in tt Production in pp Collisions at

Abstract

We present a new measurement of the inclusive forward-backward tbar{t} production asymmetry and its mass dependence. The measurements are performed with data corresponding to an integrated luminosity of L = 5.3 fb^{−1} of pp ̄ collisions at √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 tbar{t} rest frame, and in both cases are found to be consistent with CP conservation under interchange of t and bar{t}. In the tbar{t} rest frame, the asymmetry is observed to increase with the invariant mass, M_{tbar{t}}, of the tbar{t} system. Fully corrected parton-level asymmetries are derived in two regions of M_{tbar{t}}, and the asymmetry is found to be most significant at large M_{tbar{t}}. For M_{tbar{t}} ≥ 450 GeV/c2, the parton-level asymmetry in the tbar{t} rest frame is A_{tbar{t} = 0.475±0.114 compared to a next-to-leading order QCD prediction of 0.088 ± 0.013.