Screening corrections in photo and DIS production of J/Ψ

Photo and DIS production of J/Ψ are investigated and compared with calculations based on pQCD in the LLA approximation without and with screening corrections. The calculation includes corrections induced by the real part of the production amplitude, the skewed (off diagonal) gluon distribution function and the relativistic Fermi motion within the charmonium system. Our pQCD results are also compared with the predictions obtained from a Regge type two-pomeron model. Our results show that the screened pQCD model gives a better reproduction of the data than the nonscreened model. However, the available data does not enable us to exclude any of the three models we have examined. The predictions of these models, when extrapolated to both low and very high energies may provide a more effective discrimination between the different parameterizations.