Prompt Charmonium Production in Z Decays
  The color-evaporation model quantitatively describes all data on photoproduction and hadroproduction of charmonium. Although the model is in part nonperturbative, the associated parameters can for instance be determined from the charmonium photoproduction data. At this point its predictions for the prompt production of $\psi$'s at the $Z$ pole are made with no free parameters. We show here that this approach successfully describes all data on the production of prompt $\psi$'s in $Z$ decays. 
O. J. P. Eboli, E. M. Gregores, and F. Halzen