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

Abstract

We compute the $J/\psi$ polarization observables ${\lambda }_{\theta }$, ${\lambda }_{\varphi }$, ${\lambda }_{\theta \varphi }$ 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 $p_T\le 15$ 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.

Comments: 26 pages, 8 figures, accepted for publication in JHEP