Abazov, V (reprint author), Univ Buenos Aires, Buenos Aires, DF, Argentina.
We examine properties of t (t) over bar candidate events in lepton +jets final states to establish the helicities of W bosons in t -> W + b decays. Our analysis is based on a direct calculation of a probability density for each event to correspond to a t (t) over bar final state, as a function of the helicity of the W boson. Using the 125 events/pb of data collected by the DO experiment at the Fermilab Tevatron p (p) over bar Collider at root s- = 1.8 TeV, we obtain a longitudinal helicity fraction F-0 = 0.56 +/- 0.3 1, consistent with the prediction of F-0 = 0.70 from the standard model. (c) 2005 Elsevier B.V. All rights reserved.