Measurement of the forward–backward asymmetry of top-quark and antiquark pairs using the full CDF Run II data set

Abstract

We measure the forward–backward asymmetry of the production of top-quark and antiquark pairs in proton-antiproton collisions at center-of-mass energy √s = 1.96 TeV using the full data set collected by the Collider Detector at Fermilab (CDF) in Tevatron Run II corresponding to an integrated luminosity of 9.1 fb [superscript −1]. The asymmetry is characterized by the rapidity difference between top quarks and antiquarks (Δy) and measured in the final state with two charged leptons (electrons and muons). The inclusive asymmetry, corrected to the entire phase space at parton level, is measured to be A[superscript t[bar over t]][subscript FB] = 0.12 ± 0.13, consistent with the expectations from the standard model (SM) and previous CDF results in the final state with a single charged lepton. The combination of the CDF measurements of the inclusive A[superscript t][bar over t]][subscript FB] in both final states yields A[superscript t][bar over t]][subscript FB] = 0.160±0.045, which is consistent with the SM predictions. We also measure the differential asymmetry as a function of Δy. A linear fit to A[superscript t][bar over t]][subscript FB](|Δy|), assuming zero asymmetry at Δy=0, yields a slope of α =0.14 ± 0.15, consistent with the SM prediction and the previous CDF determination in the final state with a single charged lepton. The combined slope of A[superscript t][superscript t]][subscript FB] (|Δy|) in the two final states is α = 0.227±0.057, which is 2.0σ larger than the SM prediction.