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

TL;DR

This paper calculates $J/$ polarization in a CGC+NRQCD framework, showing improved agreement with low $p_T$ LHC data over traditional NLO methods, and highlighting the potential for more precise NRQCD parameter extraction.

Contribution

It introduces a combined CGC+NRQCD approach to $J/$ polarization, incorporating both color singlet and octet states, and demonstrates its effectiveness at low transverse momentum.

Findings

Better description of $J/$ polarization data at $p_T  15$ GeV

CGC+NRQCD outperforms collinear NLO calculations at low $p_T$

Framework suggests potential for improved extraction of NRQCD matrix elements

Abstract

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.