Measurement of the W polarization in t-tbar production in lepton+jets events

The W helicity fractions in top decays are measured with t-tbar events in the lepton+jets final state, using proton-proton collisions at a center-of-mass energy of 7 and 8 TeV, collected with the CMS detector at the LHC in 2011 and 2012 respectively. The measured fractions are used to probe the existence of anomalous Wtb couplings. Exclusion limits on the real components of the anomalous couplings $g_{L}$, $g_{R}$ are also derived.