Impact of QCD Energy Evolution on Observables in Heavy-Ion Collisions

TL;DR

This paper investigates how incorporating QCD small-$x$ evolution into initial state modeling affects key observables in heavy-ion collisions, highlighting the importance of nonlinear QCD effects for accurate simulations.

Contribution

It introduces the integration of JIMWLK small-$x$ evolution into the IP-Glasma framework, improving the modeling of initial conditions across different energies and rapidities.

Findings

Significant changes in particle multiplicities and spectra with small-$x$ evolution.

Altered anisotropic flow and momentum correlations due to QCD evolution.

Enhanced understanding of initial state effects on quark-gluon plasma properties.

Abstract

We study how the inclusion of energy dependence as dictated by quantum chromodynamic (QCD) small-$x$ evolution equations affects key observables in ultra-relativistic heavy-ion collisions. Specifically, we incorporate JIMWLK evolution into the IP-Glasma framework, which serves as the initial condition for a simulation pipeline that includes viscous relativistic hydrodynamics and a hadronic afterburner. This approach enables a consistent modeling of highly energetic nuclei across varying Bjorken-$x$ values, which are relevant for different collision energies and rapidity regions. In comparison to the standard IP-Glasma setup without small-$x$ evolution, we observe pronounced changes in particle multiplicities and spectral distributions, especially in smaller systems and at the highest available energies. We further explore effects on anisotropic flow observables and correlations between mean transverse momentum and elliptic flow. Our findings underscore the critical role of nonlinear QCD evolution in accurately modeling the early stages of heavy-ion collisions, as well as its implications for extracting transport properties of the quark-gluon plasma.