Measurement of W-Polarization in Di-Leptonic ttbart Events in pp Collisions with sqrt(s) = 7 TeV

We present a measurement of the W boson helicity fractions in $t\bar{t}$ events with the full dataset collected by the CMS detector in 2011 at a center-of-mass energy of $\sqrt{s}=7$~TeV. This corresponds to an integrated luminosity of $4.6\;\mathrm{fb}^{-1}$. The analysis is based on the dilepton decay channel of top pair events, in which both W bosons decay leptonically. Only events containing electrons and/or muons in the final state are considered. We measure the fractions of left-handed, longitudinal, and right-handed W boson to be $F_{L}= 0.288\pm 0.035(\text{stat})\pm 0.040(\text{sys})$ , $F_{0}= 0.698\pm 0.057(\text{stat})\pm 0.063(\text{sys})$ and $F_{R}= 0.014\pm 0.027(\text{stat})\pm 0.042(\text{sys})$. The results are consistent with the standard model predictions.