Event-by-event gluon multiplicity, energy density and eccentricities at RHIC and LHC

TL;DR

This paper uses the IP-Glasma model to compute event-by-event gluon multiplicities, energy densities, and eccentricities in heavy-ion collisions at RHIC and LHC energies, providing detailed fluctuation analysis.

Contribution

It introduces a comprehensive IP-Glasma framework combining saturation physics and classical Yang-Mills dynamics to predict multiplicity and eccentricity fluctuations without additional parameters.

Findings

Multiplicity distributions match negative binomial convolutions.

Eccentricity moments show larger odd moments compared to MC-KLN.

Fluctuation effects are significant in initial state geometry.

Abstract

The event-by-event multiplicity distribution, the energy densities and energy density weighted eccentricity moments epsilon_n (up to n=6) at early times in heavy-ion collisions at both RHIC (root-s=200 GeV) and LHC (root-s=2.76 TeV) are computed in the IP-Glasma model. This framework combines the impact parameter dependent saturation model (IP-Sat) for nucleon parton distributions (constrained by HERA deeply inelastic scattering data) with an event-by-event classical Yang-Mills description of early-time gluon fields in heavy-ion collisions. The model produces multiplicity distributions that are convolutions of negative binomial distributions without further assumptions or parameters. The eccentricity moments are compared to the MC-KLN model; a noteworthy feature is that fluctuation dominated odd moments are consistently larger than in the MC-KLN model.