Threshold expansion at order αs4 for the t(t)over-bar invariant mass distribution at hadron colliders

We calculate the leading O(alpha(4)(s)) contributions to the invariant mass distribution of top-quark pairs produced at the Tevatron and LHC, in the limit where the invariant mass of the t (t) over bar pair approaches the partonic center-of-mass energy. Our results determine at NNLO in alpha(s) the coefficients of all singular plus distributions and scale-dependent logarithms in the differential partonic cross sections for q (q) over bar .gg -> t (t) over bar +X. A numerical analysis showing the effects of the NNLO corrections on the central values and scale dependence of the invariant mass distribution is performed. The NNLO corrections are found to significantly enhance the cross section and reduce the perturbative uncertainties compared to the NLO calculation. (C) 2010 Elsevier B.V. All rights reserved.