New extraction of color-octet NRQCD matrix elements from charmonium hadroproduction

We re-analyze Tavatron data on charmonium hadroproduction in the framework of the color-octet model implemented in the event generator PYTHIA taking i nto account initial-state radiation of gluons and Altarelli/Parisi evolutio n of final-state gluons fragmenting into c (c) over bar pairs. We obtain ne w values for the color-octet matrix elements relevant to this production pr ocess. We discuss the sensitivity of our results to the transverse momentum lower cut-off employed in the generation to avoid the problematic p(t)-->0 region, arguing about the reliability of our previous extraction of the NR QCD matrix elements for the S-3(1)(8) and S-1(0)(8) +(3) P-J((8)) contribut ions. Finally we extrapolate to LHC energies to get predictions on the J/ps i direct production rate.