Wilson lines - color charge densities correlators and the production of eta' in the CGC for pp and pA collisions

TL;DR

This paper calculates eta' meson production in high-energy pp and pA collisions using the CGC framework, relating it to gluon correlators and saturation effects, providing new insights into gluon distributions and saturation scales.

Contribution

It introduces new Wilson line correlator results within the McLerran-Venugopalan model and relates eta' production to gluon correlators, advancing understanding of saturation effects in high-energy collisions.

Findings

Eta' production cross section depends on unintegrated parton distributions in pp.

In pA collisions, the cross section is sensitive to saturation effects.

The results can constrain gluon distribution models and saturation scales.

Abstract

We compute the inclusive differential cross section production of the pseudo-scalar meson eta' in high-energy proton-proton (pp) and proton-nucleus (pA) collisions. We use an effective coupling between gluons and eta' meson to derive a reduction formula that relates the eta' production to a field-strength tensor correlator. For pA collisions we take into account saturation effects on the nucleus side by using the Color Glass Condensate formalism to evaluate this correlator. We derive new results for Wilson line - color charges correlators in the McLerran-Venugopalan model needed in the computation of eta' production. The unintegrated parton distribution functions are used to characterize the gluon distribution inside protons. We show that in pp collisions, the cross section depends on the parametrization of unintegrated parton distribution functions and thus, it can be used to put constraints on these distributions. We also demonstrate that in pA collisions, the cross section is sensitive to saturation effects so it can be utilized to estimate the value of the saturation scale.