Measurement of the W helicity in t anti-t decays at s**(1/2) = 1.96 TeV in the lepton+jets final states

Two measurements of the W-helicity in t{bar t} decays at {radical}s = 1.96 TeV have been carried out using data collected by the D0 detector. Semileptonic t{bar t} events in the electron and muon channel were used. In these events the distribution of the angle between the lepton and the direction of the top measured in the rest frame of the intermediate W boson is sensitive to the helicities of the W. The two analyses differ in the usage of lifetime tag information in the event selection. With an integrated luminosity of 168:7 pb{sup -1} and 158.4 pb{sup -1} in the e+jets and {mu}+jets channels respectively, an upper limit on the fraction f{sub +} of positive helicity W's of f{sub +} < 0.244 is set by both analyses at 90% confidence level.