A complete NLO calculation of the $J/\psi$ and $\psi'$ production at hadron colliders

TL;DR

This paper presents a comprehensive NLO QCD calculation for prompt J/ψ and ψ' production at hadron colliders, demonstrating good agreement with experimental data and supporting the universality of color-octet matrix elements.

Contribution

It provides the first complete NLO calculation including both color-singlet and color-octet contributions for charmonium production at colliders.

Findings

NLO calculations align well with LHC and RHIC data.

Color-octet matrix elements show approximate universality.

Large p_T data up to 70 GeV are well described.

Abstract

A complete next-to-leading order (NLO) calculation in $\alpha_s$ for the $\jpsi$ and $\psip$ prompt production at the Tevatron, LHC, and RHIC in nonrelativistic QCD is presented. We argue that the next-to-next-to-leading order (NNLO) color-singlet contribution may not be so important as to resolve the large discrepancy between theory and experiment in $\jpsi$ large $p_T$ production cross sections. Therefore, a complete NLO calculation, including both color-singlet and color-octet contribution, is necessary and essential to give a good description for $\jpsi$ and $\psip$ production. We also study the methods to fit the long-distance matrix elements using either two linear combined matrix elements or three matrix elements, and find these two methods can give consistent results. Compared with the measurements at the LHC and RHIC for prompt $\jpsi$ and $\psip$ production, our predictions are found to agree with all data. In particular, the recently released large $p_T$ data (up to 60-70 GeV) at the LHC are in good agreement with our predictions. Our results imply that the universality of color-octet matrix elements holds approximately in charmonium hadroproduction, when one uses fixed order perturbative calculation to describe data (the data in small $p_T$ region are not included). Our work may provide a new test for the universality of color-octet matrix elements, and the color-octet mechanism in general.