High energy factorization in nucleus-nucleus collisions

TL;DR

This paper develops a high energy factorization theorem for inclusive gluon production in nucleus-nucleus collisions, incorporating all leading logarithmic and density-enhanced contributions, and links it to the JIMWLK evolution of nuclear wavefunctions.

Contribution

It derives a comprehensive factorization formula for gluon production in A+A collisions, connecting it with the JIMWLK evolution and providing a new derivation of the Hamiltonian using retarded Green's functions.

Findings

Resummed inclusive gluon spectrum as a convolution of gauge invariant distributions.

Distributions satisfy the JIMWLK evolution equation.

JIMWLK Hamiltonian derived from retarded Green's functions.

Abstract

We derive a high energy factorization theorem for inclusive gluon production in A+A collisions. Our factorized formula resums i) all order leading logarithms (g^2 \ln(1/x_{1,2}))^n of the incoming partons momentum fractions, and ii) all contributions (g \rho_{1,2})^n that are enhanced when the color charge densities in the two nuclei are of order of the inverse coupling-- \rho_{1,2}\sim g^{-1}. The resummed inclusive gluon spectrum can be expressed as a convolution of gauge invariant distributions W[\rho_{1,2}] from each of the nuclei with the leading order gluon number operator. These distributions are shown to satisfy the JIMWLK equation describing the evolution of nuclear wavefunctions with rapidity. As a by-product, we demonstrate that the JIMWLK Hamiltonian can be derived entirely in terms of retarded light cone Green's functions without any ambiguities in their pole prescriptions. We comment on the implications of our results for understanding the Glasma produced at early times in A+A collisions at collider energies.