Longitudinal, transverse-plus and transverse-minus W bosons in unpolarizedtop quark decays at O(alpha(s)) - art. no. 031501

We consider the O(alpha (s)) radiative corrections to the decay of an unpol arized top quark into a bottom quark and a W-gauge boson where the heliciti es of the W are specified as longitudinal, transverse plus and transverse-m inus. The O(alpha (s)) radiative corrections lower the normalized longitudi nal rate Gamma (L)/Gamma by 1.06% and increase the normalized transverse-mi nus rate Gamma_/Gamma by 2.17%. We find that the normalized transverse-plus rate Gamma (+)/Gamma, which vanishes at the Born term level for m(b)-->0, receives radiative correction contributions at the sub-percent level. We di scuss m(b)not equal0 effects for the Born term and the alpha (s)-contributi ons. but find these to be small. Our results are discussed in light of rece nt measurements of the helicity content of the W in top quark decays by the CDF Collaboration.