Next-to-leading order QCD corrections to top quark spin correlations at hadron colliders: The Reactions $gg \to t \overline t(g)$ and $gq(\overline q) \to t \overline tq(\overline q)$

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