Helicity fractions of W bosons from top quark decays at NNLO in QCD
arXiv:1005.2625 · doi:10.1103/PhysRevD.81.111503
Abstract
Decay rates of unpolarized top quarks into longitudinally and transversally polarized W bosons are calculated to second order in the strong coupling constant alpha_s. Including the finite bottom quark mass and electroweak effects, the Standard Model predictions for the W boson helicity fractions are F_L=0.687(5), F_+=0.0017(1), and F_-=0.311(5).
5 pages, 1 figure