  A measurement of the W boson helicity is presented, where the W boson
originates from the decay of a top quark produced in pp collisions. The event
selection, optimized for reconstructing a single top quark in the final state,
requires exactly one isolated lepton (muon or electron) and exactly two jets,
one of which is likely to originate from the hadronization of a bottom quark.
The analysis is performed using data recorded at a center-of-mass energy of 8
TeV with the CMS detector at the CERN LHC in 2012. The data sample corresponds
to an integrated luminosity of 19.7 inverse femtobarns. The measured helicity
fractions are F[L] = 0.298 +/- 0.028 (stat) +\- 0.032 (syst), F[0] = 0.720 +/-
0.039 (stat) +/- 0.037 (syst), and F[R] = -0.018 +/- 0.019 (stat) +/- 0.011
(syst). These results are used to set limits on the real part of the tWb
anomalous couplings, gL and gR.
