Forward-Backward Asymmetry in Top-Quark Production in $p\overline{p}$ Collisions at $\sqrt{s}=1.96\mathrm{TeV}$

We present measurements of the forward-backward charge asymmetry in top pair production using $1.9{\mathrm{fb}}^{-1}$ of $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ recorded with the Collider Detector at Fermilab II. Correcting for acceptance and measurement dilutions we obtain parton-level asymmetries of $A_{\mathrm{FB}}^{p\overline{p}}=0.17\pm 0.08$ in the $p\overline{p}$ frame and $A_{\mathrm{FB}}^{t\overline{t}}=0.24\pm 0.14$ in the $t\overline{t}$ frame. The values are consistent with the standard model expectation and disfavor exotic production mechanisms with significant negative values.

Figure 1

The two top-quark production angle variables, $\cos \theta$ for the $p\overline{p}$ frame and $\Delta Y$ for the $t\overline{t}$ frame. The solid line is the prediction for $t\overline{t}$ with mc@nlo model of the QCD-induced charge asymmetry and ${\sigma }_{t\overline{t}}=8.2\mathrm{pb}$, plus the expected $\mathrm{non}\mathrm{\text{−}}t\overline{t}$ backgrounds. The dashed curve shows the prediction when $t\overline{t}$ is reweighted according to the form $1+A_{\mathrm{FB}}\cos \alpha$ using measured values of $A_{\mathrm{FB}}$.