Measurement of the leptonic asymmetry in $t\overline{t}$ events produced in $p\overline{p}$ collisions at $\sqrt{s}\mathbf{=}1.96\mathrm{TeV}$

We measure the asymmetry in the charge-weighted rapidity $q{y}_{\ell }$ of the lepton in semileptonic $t\overline{t}$ decays recorded with the CDF II detector using the full Tevatron Run II sample, corresponding to an integrated luminosity of $9.4{\mathrm{fb}}^{-1}$. A parametrization of the asymmetry as a function of $q{y}_{\ell }$ is used to correct for the finite acceptance of the detector and recover the production-level asymmetry. The result of $A_{\mathrm{FB}}^{\ell }={0.094}_{-0.029}^{+0.032}$ is to be compared to the standard model next-to-leading-order prediction of $A_{\mathrm{FB}}^{\ell }=0.038\pm 0.003$.

Figure 1

The distribution of simulated $t\overline{t}$ events vs $q{y}_{\ell }$ at the production level for several models. The vertical lines at $|q{y}_{\ell }|=1.25$ indicate the limits of the lepton acceptance.

Figure 2

The distribution of events vs $q{y}_{\ell }$ in the zero-tag control sample. Black markers indicate the data. The filled region represents the prediction of $t\overline{t}$ (light-colored fill) and backgrounds (dark).

Figure 3

The symmetric part (a) and asymmetry (b) of the production-level distribution of $q{y}_{\ell }$ for the discussed models. Shown also are the best fits to Eq. (7). The vertical lines at $|q{y}_{\ell }|=1.25$ indicate the limits of the lepton acceptance.

Figure 4

The distribution of candidate events in the signal region vs the measured $p_T$ of the lepton.

Figure 5

The observed distribution of events vs $q{y}_{\ell }$ in the signal region (a) compared to the NLO QCD prediction of powheg and backgrounds; (b) after subtracting backgrounds, compared to the NLO QCD prediction of powheg.

Figure 6

The symmetric part (a) and asymmetry (b) as function of $q{y}_{\ell }$ resulting from the decomposition of Fig. 5. Data are shown as black markers, compared to the light-colored NLO QCD prediction of powheg.

Figure 7

The binned asymmetry $A_{\mathrm{FB}}^{\ell }(q{y}_{\ell })$ after correcting for acceptance, compared to the NLO QCD prediction of powheg. The best fit to Eq. (7) for each is shown as the smooth curve of the same color. The dark (light) gray bands indicate the statistical (total) uncertainty on the fit curve to the data.