Quarkonium Production in an Improved Color Evaporation Model

We propose an improved version of the color evaporation model to describe heavy quarkonium production. In contrast to the traditional color evaporation model, we impose the constraint that the invariant mass of the intermediate heavy quark-antiquark pair to be larger than the mass of produced quarkonium. We also introduce a momentum shift between heavy quark-antiquark pair and the quarkonium. Numerical calculations show that our model can describe the charmonium yields as well as ratio of $\psi^\prime$ over $J/\psi$ better than the traditional color evaporation model.Comment: 6 pages, 4 figure

J/ψJ/\psi polarization in the CGC+NRQCD approach

We compute the $J/\psi$ polarization observables $\lambda_\theta$, $\lambda_\phi$, $\lambda_{\theta\phi}$ in a Color Glass Condensate (CGC) + nonrelativistic QCQ (NRQCD) formalism that includes contributions from both color singlet and color octet intermediate states. Our results are compared to low $p_T$ data on $J/\psi$ polarization from the LHCb and ALICE experiments on proton-proton collisions at center-of-mass energies of $\sqrt{s}=7$ TeV and 8 TeV. Our CGC+NRQCD computation provides a better description of data for $p_T \leq 15$ GeV relative to extant next-to-leading (NLO) calculations within the collinear factorization framework. These results suggest that higher order computations in the CGC+NRQCD framework have the potential to greatly improve the accuracy of extracted values of the NRQCD universal long distance matrix elements.Comment: 26 pages, 8 figures, accepted for publication in JHE