PRODUCTION OF HEAVY QUARKONIUM IN HIGH-ENERGY COLLIDERS

Recent data from the Tevatron collider have revealed that the producti on rate of prompt charmonium at large transverse momentum is orders of magnitude larger than the best theories of a few years ago had predic ted. These surprising results can be understood by taking into account two recent developments that have dramatically revised the theoretica l description of heavy-quarkonium production. The first is the realiza tion that fragmentation must dominate at large transverse momentum, wh ich implies that most charmonium in this kinematic region is produced by the hadronization of individual high-pr partons. The second is the development of a factorization formalism for quarkonium production bas ed on nonrelativistic QCD that allows the formation of charmonium from color-octet c (c) over bar pairs to be treated systematically. This r eview summarizes these theoretical developments and their implications for quarkonium production in high-energy colliders.