Soft and hard QCD in charmonium production

Abstract

Hard and soft QCD dynamics are both important in charmonium hadroproduction, as presented here through a next-to-leading order QCD matrix element calculation combined with the colour evaporation model. Observed $x_F$ and $p_\perp$ distributions of $J/\psi$ in hadroproduction are reproduced. Quite similar results can also be obtained with a Monte Carlo event generator where \ccbar pairs are instead produced through leading order matrix elements and the parton shower approximation of higher order processes. The soft dynamics may alternatively be described by the soft colour interaction model. We also discuss the relative rates of different charmonium states and introduce an improved model for mapping the continuous ccbar mass spectrum on the physical charmonium resonances.Comment: Presented at Pan American Advanced Studies Institute (PASI 2002), Campos do Jord\~ao, Brazil, January 7-18, 200