| A measurement of the fraction, f+, of right-handed W bosons produced in top quark decays is presented. This analysis is based on a sample corresponding to an integrated luminosity of 370 pb-1, collected by the DO detector at the Fermilab Tevatron pp¯ Collider at s = 1.96 TeV. The helicity angle, theta*, is reconstructed for each lepton. f+ is determined by comparing the cos theta* distribution from the data with that for the expected background and signal for various values of f+. The fraction of longitudinal W bosons, f0, is assumed to be 0.7 as predicted by the standard model. This yields f+ = 0.109 +/- 0.094 (stat) +/- 0.063 (syst), consistent with the standard model prediction of f+ = 3.6 x 10-4 . The possibility that both f+ and f0 stray from standard model values is also investigated. In this case cos theta* distributions for each possible W helicity state, along with the backgrounds, are fit to the cos theta* distribution for the data. The best fit values are f+ = 0.82 +/- 0.30(stat) and f0 = -0.58 +/- 0.50(stat). |
