New extraction of color-octet NRQCD matrix elements from charmonium hadroproduction
Abstract
We re-analyze Tavatron data on charmonium hadroproduction in the framework of the color-octet model implemented in the event generator PYTHIA taking into account initial-state radiation of gluons and Altarelli-Parisi evolution of final-state gluons fragmenting into cc pairs. We obtain new values for the color-octet matrix elements relevant to this production process. We discuss the sensitivity of our results to the transverse momentum lower cut-off employed in the generation to avoid the problematic pt0 region, arguing about the reliability of our previous extraction of the NRQCD matrix elements for the 3S1(8) and 1S0(8)+3PJ(8) contributions. Finally we extrapolate to LHC energies to get predictions on the J/ direct production rate.
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