The classical field created in early stages of high energy nucleus-nucleus collisions

TL;DR

This paper introduces a simplified method using a specific light-cone gauge to calculate the initial classical color field in high-energy nucleus-nucleus collisions, providing explicit formulas for gluon spectra.

Contribution

It presents a novel gauge choice that simplifies the calculation of the classical color field and derives an explicit gluon spectrum formula in nucleus-nucleus collisions.

Findings

Exact calculation of the initial color field after collision

Derivation of a simple gluon spectrum formula

Recovery of $k_t$-factorization in proton-nucleus collisions

Abstract

We show that a special choice of light-cone gauge can greatly simplify the calculation of the classical color field created in the initial stages of nucleus-nucleus collisions. Within this gauge, we can in particular construct explicitly the conserved color current and calculate exactly the gauge field immediately after the collision. This field is used as a boundary condition in an iterative solution of the Yang-Mills equations in the forward light-cone. In leading order, which corresponds to a linearization of the Yang-Mills equation in the forward light-cone, we obtain a simple formula for the spectrum of gluons produced in nucleus-nucleus collisions. This formula reproduces exactly the known formula for proton-nucleus collisions, where $k_t-$factorization is recovered, while the latter property apparently breaks down in the case of nucleus-nucleus collisions.