Systematics of quarkonium production

Quarkonium production in high-energy reactions is found to exhibit a behaviour more universal than that expected from velocity scaling. Total rates of quarkonia produced in hadronic interactions as well as Feynman-x and transverse momentum distributions can be described over the full range of accessible energies (15 ≲ s ≲ 1800 GeV) by two-stage processes. The quarkonium production cross section factors into a process-dependent short-distance part and a single long-distance matrix element. The first part describing the production of a free quark-antiquark pair is the perturbatively calculated subthreshold cross section. The non-perturbative factor turns out to be universal, giving the model great predictive power. Furthermore we estimate the fraction of the heavy-quark cross section leading to quarkonium for both the charm and bottom systems. Finally, we comment on quarkonium photoproduction.