A search for non-standard model W helicity in top quark decays

The structure of the tbW vertex is probed by measuring the polarization of the W in t → W + b → l + v + b. The invariant mass of the lepton and b quark measures the W decay angle which in turn allows a comparison with polarizations expected from different possible models for the spin properties of the tbW interaction. We measure the fraction by rate of Ws produced with a V + A coupling in lieu of the Standard Model V-A to be fV + A = -0.21+0.42-0.24 (stat) +/- 0.21 (sys). We assign a limit of fV + A < 0.80 95% Confidence Level (CL). By combining this result with a complementary observable in the same data, we assign a limit of fV + A < 0.61 95% CL. We find no evidence for a non-Standard Model tbW vertex.