Charmonium Production

Abstract

Theoretical analyses of the results on quarkonium production at large transverse momentum ($p_T$) in $p\bar p$ collisions, at the Tevatron have revealed two novel features of the physics of quarkonium production : 1) the contribution of fragmentation of gluons and charm quarks to the cross-section at large $p_T$, and 2) the importance of colour octet components of the quarkonium wave-function. I discuss the theoretical developments which have contributed to a reasonably consistent picture of quarkonium production at the Tevatron, and discuss large-$p_T$ $J/\psi$ production at HERA and at LHC as important tests of the fragmentation picture. I also discuss our recent analysis of $J/\psi$ production cross-sections at fixed-target energies, where we find that the energy dependence of the $p_T$-integrated cross-sections for both $pp$ and $\pi^- - p$ collisions is reasonably well reproduced, when the colour-octet components are included.