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 $t\overline{t}$ production asymmetry, ${A}_{\mathrm{FB}}$, and its dependence on several properties of the $t\overline{t}$ system. The measurements are performed with the full Tevatron data set recorded with the CDF II detector during $p\overline{p}$ collisions at $\sqrt{s}=1.96\text{ }\text{ }\mathrm{TeV}$, corresponding to an integrated luminosity of $9.4\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$. We measure the asymmetry using the rapidity difference $\ensuremath{\Delta}y={y}_{t}\ensuremath{-}{y}_{\overline{t}}$. Parton-level results are derived, yielding an inclusive asymmetry of $0.164\ifmmode\pm\else\textpm\fi{}0.047(\mathrm{stat}+\mathrm{syst})$. We establish an approximately linear dependence of ${A}_{\mathrm{FB}}$ on the top-quark pair mass ${M}_{t\overline{t}}$ and the rapidity difference $|\ensuremath{\Delta}y|$ at detector and parton levels. Assuming the standard model, the probabilities to observe the measured values or larger for the detector-level dependencies are $7.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ and $2.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ for ${M}_{t\overline{t}}$ and $|\ensuremath{\Delta}y|$ respectively. Lastly, we study the dependence of the asymmetry on the transverse momentum of the $t\overline{t}$ 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.