Combined Forward-Backward Asymmetry Measurements in Top-Antitop Quark Production at the Tevatron

The CDF and D0 experiments at the Fermilab Tevatron have measured the asymmetry between yields of forward- and backward-produced top and antitop quarks based on their rapidity difference and the asymmetry between their decay leptons. These measurements use the full data sets collected in proton-antiproton collisions at a center-of-mass energy of $\sqrt{s}=1.96\mathrm{TeV}$. We report the results of combinations of the inclusive asymmetries and their differential dependencies on relevant kinematic quantities. The combined inclusive asymmetry is $A_{\mathrm{FB}}^{t\overline{t}}=0.128\pm 0.025$. The combined inclusive and differential asymmetries are consistent with recent standard model predictions.

Figure 1

Results for $A_{\mathrm{FB}}^{t\overline{t}}$ vs $m_{t\overline{t}}$ for the individual CDF and D0 measurements and for their combination. The inputs to the combination are displaced at different abscissa values within each $m_{t\overline{t}}$ bin for ease of visibility. The inner error bar indicates the statistical uncertainty, while the outer error bar corresponds to the total uncertainty including the systematic uncertainty added in quadrature. The value of the combined data point for the mass region of $550–650\mathrm{GeV}/c^2$ is discussed in Ref. [31] in more detail. The linear dependence of the combined result is given by the solid black line together with the 1 SD total uncertainty of the two-parameter fit given by the shaded gray area. The dashed orange line shows the NNLO $\mathrm{QCD}+\mathrm{NLO}\mathrm{EW}$ prediction of Refs. [1, 2, 26], while the shaded orange area reflects its 1 SD uncertainty.

Figure 2

Measurements of the differential asymmetries $A_{\mathrm{FB}}^{t\overline{t}}$ vs $|\mathrm{\Delta }{y}_{t\overline{t}}|$ with data points displayed at the distribution-weighted center of the bins. The inner error bar indicates the statistical uncertainty, while the outer error bar corresponds to the total uncertainty, including the systematic uncertainty added in quadrature. The combined linear dependence for all the experimental results is given by the solid black line, with the 1 SD total uncertainty on the one-parameter fit given by the shaded gray area. The dashed orange line shows the NNLO $\mathrm{QCD}+\mathrm{NLO}\mathrm{EW}$ prediction [1, 2, 26], while the shaded orange area reflects its 1 SD uncertainty.

Figure 3

Comparison of the differential asymmetries $A_{\mathrm{FB}}^{\ell }$ as a function of $|q_{\ell }{\eta }_{\ell }|$ displayed at the center of the bins. The left-most data point of the CDF $\ell +\text{jets}$ data is slightly moved right to avoid direct overlap with the left-most data point of the $\mathrm{D}0\ell +\text{jets}$ data. Each error bar represents the total experimental uncertainty. The dashed orange line shows the NLO SM prediction [3, 32], while the shaded orange area shows its 1 SD uncertainty.

Figure 4

Comparison of the differential asymmetries $A_{\mathrm{FB}}^{\ell \ell }$ as a function of $|\mathrm{\Delta }\eta |$ displayed at the center of the bins. Each error bar represents the total experimental uncertainty. The dashed orange line shows the NLO SM prediction [3, 32], while the shaded orange area shows its 1 SD uncertainty.

Figure 5

Summary of inclusive forward-backward asymmetries in $t\overline{t}$ events in percents at the Tevatron.