ON THE THRESHOLD BEHAVIOR OF HEAVY TOP PRODUCTION

If the top is heavy, as now seems likely, the ttBAR threshold behaviour is given by perturbative QCD. The QCD threshold interaction can be formulated in terms of a potential, attractive or repulsive depending on whether the ttBAR is in a colour singlet or octet state. This gives a suppression factor for octet production. Singlet production is enhanced, both above threshold and, by resonance formation, below it. While e+ e- annihilation only proceeds in the singlet ttBAR channel, hadron-hadron collisions contain a non-trivial mixture of the two. In this paper we review the relevant threshold factor formulae, and present phenomenological consequences for hadron colliders, current and future.