W boson polarization measurement in the ttbar dilepton channel using the CDF II Detector

We present a measurement of $W$ boson polarization in top-quark decays in $t\bar{t}$ events with decays to dilepton final states using $5.1 {\rm fb^{-1}}$ofintegratedluminosityin$p\bar{p}$ collisions collected by the CDF II detector at the Tevatron. A simultaneous measurement of the fractions of longitudinal ($f_0$) and right-handed ($f_{+}$) $W$ bosons yields the results $f_0=0.71_{-0.17}^{+0.18}(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t})\pm 0.06(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t})$ and $f_+ = -0.07 \pm 0.09 {\rm (stat)} \pm 0.03 {\rm (syst)}$. Combining this measurement with our previous result based on single lepton final states, we obtain $f_0 = 0.84 \pm 0.09 {\rm (stat)} \pm 0.05 {\rm (syst)}$and$f_{+} = -0.16 \pm 0.05 {\rm (stat)} \pm 0.04 {\rm (syst)}$. The results are consistent with standard model expectation.