NNLO QCD corrections to the polarized top quark decay $t(\uparrow) \to X_b+W^+$

Abstract

We compute the next-to-next-to-leading order (NNLO) QCD corrections to the decay $t(\uparrow) \to X_b +W^+$ of a polarized top quark. The spin-momentum correlation in this quasi two-body decay is described by the polar angle distribution $\mathrm{d}Γ/\mathrm{d}\cosθ_P=\fracΓ{2}(1+P_t\, α_P\, \cosθ_P)$ where $P_t$ is the polarization of the top quark and $α_P$ denotes the asymmetry parameter of the decay. For the latter we find $α^{\mathrm{NNLO}}_P=0.3792\pm 0.0037$.

17 pages, 3 figures; v2: added Fig. 2 and 3 and corresponding discussion