Top quark production at threshold with O(αs2) accuracy Original Research Article

We calculate the next-to-next-to-leading order correction to the cross section for top quark pair production in e+e− annihilation in the threshold region, resumming all O[(αs/β)n × (αs2, β2, αsβ)] terms of perturbation series. We find that the magnitude of the NNLO correction is comparable to the size of the NLO corrections.