We present the results of our analysis on charmonia (J/ψ and ψ ′ ) hadroproduction taking into account higher-order QCD effects induced by initial-state radiation in a Monte Carlo framework, with the colour-octet mechanism implemented in the event generation. We find that those colour-octet matrix elements extracted so far from Fermilab Tevatron data for both J/ψ and ψ ′ production have to be lowered significantly. We finally make predictions for charmonia production at the LHC, presenting a simple code for a fast simulation with PYTHIA based on the colour-octet model.

We firstly re-examine hadroproduction of prompt J/ψ's at the Fermilab Tevatron finding that those colour-octet matrix elements presented in literature are systematically overestimated due to the overlooking of the effective primordial transverse momentum of partons (i.e. dynamically generated via initial-state radiation). We estimate the size of these effects using different parton distribution functions in a Monte Carlo framework. Finally, we extrapolate up to LHC energies making a prediction on the expected p t differential cross-section for charmonium.

We firstly examine hadroproduction of prompt J/ψ's at the Fermilab Tevatron in a Monte Carlo framework by means of the event generator PYTHIA 5.7 in which those colour-octet processes relevant for charmonium production have been implemented accordingly. We find that colour-octet matrix elements presented in literature from pp collider data are systematically overestimated due to overlooking of the effective primordial transverse momentum of partons (i.e. including higher-order QCD effects). We estimate the size of these effects using different parton distribution functions. Finally, after normalization to Tevatron data, we extrapolate up to LHC energies making a prediction on the expected pt differential cross-section for charmonium.