Production and polarization of direct $J/\psi$ to ${\mathcal O}(\alpha_s^3)$ in the improved color evaporation model in collinear factorization

TL;DR

This paper computes the production and polarization of direct J/ψ mesons at order α_s^3 within the improved color evaporation model, providing new polarization predictions in different frames and matching experimental data at moderate transverse momentum.

Contribution

It presents the first calculation of polarization parameters for J/ψ in the improved color evaporation model at this order in collinear factorization.

Findings

Agreement with J/ψ cross sections at small and moderate p_T.

First predictions of polarization parameters in multiple frames.

Frame-invariant polarization parameter matches experimental trends.

Abstract

We calculate the production and polarization of direct $J/\psi$ in the improved color evaporation model at $\mathcal{O}(\alpha_s^3)$ in the collinear factorization approach. We present the first calculation of polarization parameters $\lambda_\vartheta$, $\lambda_{\phi}$, and $\lambda_{\vartheta \phi}$ in the helicity and the Collins-Soper frames, as well as the frame-invariant polarization parameter $\tilde{\lambda}$ as a function of transverse momentum. We find agreement with both $J/\psi$ cross sections and the invariant polarization parameters at small and moderate $p_T$.