Gluon spectrum in the glasma from JIMWLK evolution

TL;DR

This paper numerically solves the JIMWLK equation with a running coupling to analyze the gluon spectrum in the glasma, revealing energy-dependent spectral hardening and multiplicity growth in high-energy heavy ion collisions.

Contribution

It introduces a numerical solution of the JIMWLK equation with a daughter dipole running coupling and applies it to compute gluon spectra in the glasma, highlighting spectral and multiplicity evolution.

Findings

Gluon spectrum becomes harder with increasing energy.

The ratio of mean gluon transverse momentum to saturation scale increases with energy.

Total gluon multiplicity grows slightly faster than saturation scale squared.

Abstract

The JIMWLK equation with a "daughter dipole" running coupling is solved numerically starting from an initial condition given by the McLerran-Venugopalan model. The resulting Wilson line configurations are then used to compute the spectrum of gluons comprising the glasma inital state of a high energy heavy ion collision. The development of a geometrical scaling region makes the spectrum of produced gluons harder. Thus the ratio of the mean gluon transverse momentum to the saturation scale grows with energy. Also the total gluon multiplicity increases with energy slightly faster than the saturation scale squared.