Next-to-leading order QCD corrections to top quark spin correlations at hadron colliders: the reactions gg→tt̄(g) and gq(q̄)→tt̄q(q̄)

We have computed the cross section for tt̄ production by gluon–gluon fusion at next-to-leading order (NLO) in the QCD coupling, keeping the full dependence on the tt̄ spins. Furthermore, we have determined to the same order the spin dependent cross sections for the processes g+q(q̄)→tt̄+q(q̄). Together with our previous results [Phys. Lett. B 483 (2000) 99] for q+q̄→tt̄(g) these results allow for predictions, at NLO QCD, of the hadronic production of tt̄ pairs in a general spin configuration. As an application we have determined the degree of correlation of the t and t̄ spins at NLO, using various spin quantisation axes.