Measurement of the top quark forward-backward production asymmetry and its dependence on event kinematic properties

Abstract

We present new measurements of the inclusive forward-backward t¯t production asymmetry, AFB, and its dependence on several properties of the t¯t system. The measurements are performed with the full Tevatron data set recorded with the CDF II detector during p¯p collisions at √s=1.96 TeV, corresponding to an integrated luminosity of 9.4 fb−1. We measure the asymmetry using the rapidity difference Δy=yt−y¯t. Parton-level results are derived, yielding an inclusive asymmetry of 0.164±0.047(stat+syst). We establish an approximately linear dependence of AFB on the top-quark pair mass Mt¯t and the rapidity difference |Δy| at detector and parton levels. Assuming the standard model, the probabilities to observe the measured values or larger for the detector-level dependencies are 7.4×10−3 and 2.2×10−3 for Mt¯t and |Δy| respectively. Lastly, we study the dependence of the asymmetry on the transverse momentum of the t¯t system at the detector level. These results are consistent with previous lower-precision measurements and provide additional quantification of the functional dependencies of the asymmetry.