Color-neutral heavy particle production in nucleus-nucleus collisions in the quasi-classical approximation

TL;DR

This paper develops a diagrammatic approach to analyze the production of color-neutral heavy particles in nucleus-nucleus collisions within a quasi-classical framework, emphasizing gluon distributions and momentum factorization.

Contribution

It introduces a symmetric treatment of colliding nuclei using Coulomb gauge and demonstrates transverse momentum factorization in a quasi-classical approximation without small-x evolution.

Findings

Cross section factorizes into gluon distributions at saturation momentum

Transverse momentum broadening described as a diffusion process

Momentum factorization is gauge-dependent but confirmed in covariant gauge

Abstract

We use a diagrammatic approach to study color-neutral heavy particle production in nucleus-nucleus collisions in a quasi-classical approximation without small-$x$ evolution. In order to treat the two nuclei symmetrically, we use the Coulomb gauge which gives the appropriate light cone gauge for each nucleus. The resulting cross section is factorized into a product of two Weizs\"{a}cker-Williams gluon distributions of the two nuclei when the transverse momentum of the produced scalar particle is around the saturation momentum. We confirm our results in covariant gauge where the transverse momentum broadening of hard gluons can be described as a diffusion process. The transverse momentum factorization manifests itself in light cone gauge but not so clearly in covariant gauge.