We present a simultaneous measurement of the forward-backward asymmetry and the top-quark polarization in $t\overline{t}$ production in dilepton final states using $9.7{\mathrm{fb}}^{-1}$ of proton-antiproton collisions at $\sqrt{s}=1.96\mathrm{TeV}$ with the D0 detector. To reconstruct the distributions of kinematic observables we employ a matrix element technique that calculates the likelihood of the possible $t\overline{t}$ kinematic configurations. After accounting for the presence of background events and for calibration effects, we obtain a forward-backward asymmetry of $A^{t\overline{t}}=(15.0\pm 6.4(\text{stat})\pm 4.9(\text{syst}))\%$ and a top-quark polarization times spin analyzing power in the beam basis of $\kappa P=(7.2\pm 10.5(\text{stat})\pm 4.2(\text{syst}))\%$, with a correlation of $-56\%$ between the measurements. If we constrain the forward-backward asymmetry to its expected standard model value, we obtain a measurement of the top polarization of $\kappa P=(11.3\pm 9.1(\text{stat})\pm 1.9(\text{syst}))\%$. If we constrain the top polarization to its expected standard model value, we measure a forward-backward asymmetry of $A^{t\overline{t}}=(17.5\pm 5.6(\text{stat})\pm 3.1(\text{syst}))\%$. A combination with the D0 $A^{t\overline{t}}$ measurement in the $\text{lepton}+\text{jets}$ final state yields an asymmetry of $A^{t\overline{t}}=(11.8\pm 2.5(\text{stat})\pm 1.3(\text{syst}))\%$. Within their respective uncertainties, all these results are consistent with the standard model expectations.

• Received 22 July 2015

DOI:https://doi.org/10.1103/PhysRevD.92.052007