%0 Journal Article
%T Analytical results for $e^+e^-\to t\bar t$ and $¦Ã¦Ã\to t\bar t$ observables near the threshold up to the next-to-next-to-leading order of NRQCD
%A A. A. Penin
%A A. A. Pivovarov
%J Physics
%D 1999
%I arXiv
%R 10.1134/1.1349450
%X We present an analytical description of top-antitop pair production near the threshold in $e^+e^-$ annihilation and $\g\g$ collisions. A set of basic observables considered includes the total cross sections, forward-backward asymmetry and top quark polarization. The threshold effects relevant for the basic observables are described by three universal functions related to S wave production, P wave production and S-P interference. These functions are computed analytically up to the next-to-next-to-leading order of NRQCD. The total $e^+e^-\to t\bar t$ cross section near the threshold is obtained in the next-to-next-to-leading order in the closed form including the contribution due to the axial coupling of top quark and mediated by the Z-boson. The effects of the running of the strong coupling constant and of the finite top quark width are taken into account analytically for the P wave production and S-P wave interference.
%U http://arxiv.org/abs/hep-ph/9904278v4