  The W-boson helicity fractions in top-quark decays are measured with ttbar
events in the lepton+jets final state, using proton-proton collisions at a
centre-of-mass energy of 7 TeV, collected in 2011 with the CMS detector at the
LHC. The data sample corresponds to an integrated luminosity of 5.0 inverse
femtobarns. The measured fractions of longitudinal, left-, and right-handed
helicity are F0 = 0.682 +/- 0.030 (stat.) +/- 0.033 (syst.), FL = 0.310 +/-
0.022 (stat.) +/- 0.022 (syst.), and FR = 0.008 +/- 0.012 (stat.) +/- 0.014
(syst.), consistent with the standard model predictions. The measured fractions
are used to probe the existence of anomalous Wtb couplings. Exclusion limits on
the real components of the anomalous couplings gL, gR are also derived.
