Measurement of the W-boson helicity in top decays from ttbar production in lepton+jets events at the LHC at sqrt(s)=8 TeV

This note reports on the measurement of the W-boson helicity fractions in decays of $\rm{t \bar t}$ into the muon+jets channel, using a sample of events from proton-proton collisions at a centre-of-mass energy of 8 TeV, collected in 2012 with the CMS detector at the LHC. The sample corresponds to an integrated luminosity of 19.6 fb$^{-1}$. The measured fractions are $F_0=0.659\pm 0.015$ (stat.) $\pm 0.023$ (syst.), $F_L=0.350\pm 0.010$ (stat.) $\pm 0.024$ (syst.), and $F_R=-0.009 \pm 0.006$ (stat.) $\pm 0.020$ (syst.), consistent with the standard model expectations.