Measurement of the Angular Distribution of Electrons fromW ! e Decays Observed in p p Collisions at ps = 1 : 8

3 We present the rst measurement of the electron angular distribution parameter 2 in W ! ee events produced in proton-antiproton collisions as a function of the W boson transverse momentum. Our analysis is based on data collected using the DD detector during the 1994{1995 Fermilab Tevatron run. We compare our results with next-to-leading order perturbative QCD, which predicts an angular distribution of (1 1 cos + 2 cos 2), where is the polar angle of the electron in the Collins-Soper frame. In the presence of QCD corrections, the parameters 1 and 2 become functions of p W T , the W boson transverse momentum. This measurement provides a test of next-to-leading order QCD corrections which are a non-negligible contribution to the W boson mass measurement.