O(alpha(2)(s)) corrections to e(+)e(-)-> t(t)over-bar total and differential cross sections near threshold - art. no. 114014

Recently full O(alpha(s)(2),alpha(s)beta,beta(2)) corrections to the thresh old total cross section for e(+)e(-) --> t (t) over bar have been calculate d, and the reported corrections turned out to be unexpectedly large. We stu dy how to reduce the theoretical uncertainties of the cross section. We ado pt a new mass definition proposed by Beneke, which incorporates a renormalo n-pole cancellation in the total energy of a static quark-antiquark pair. T his improves the convergence of the 1S resonance mass, while the normalizat ion of the cross section scarcely changes. We argue that resummations of lo garithms are indispensable, since two largely separated scales dictate the shape of the cross section. As a first step, we resum logarithms in the Cou lombic part of the t (t) over bar potential, and observe a considerable imp rovement in the convergence of corresponding corrections. There still remai n, however, large corrections, which arise from a 1/r(2) term in the t (t) over bar potential. We also calculate full O(alpha(s)(2),alpha(s)beta,beta( 2)) corrections to the momentum distributions of top quarks in the threshol d region. Corrections to the distribution shape are of moderate size over t he whole threshold region. [S0556-2821(99)02321-8].