Model comparison for initial density fluctuations in high energy heavy ion collisions

TL;DR

This paper compares four models for initial density fluctuations in high energy heavy ion collisions, analyzing their statistical properties and correlations to understand universal behaviors and differences.

Contribution

It introduces a Fourier-Bessel mode expansion for fluctuations and compares multiple models, including an analytically solvable one, to identify universal features.

Findings

Large wavelength modes show universal properties across models.

Analytical insights into initial condition properties are possible.

Differences among models are characterized by correlation functions.

Abstract

Four models for the initial conditions of a fluid dynamic description of high energy heavy ion collisions are analysed and compared. We study expectation values and event-by-event fluctuations in the initial transverse energy density profiles from Pb-Pb collisions. Specifically, introducing a Fourier-Bessel mode expansion for fluctuations, we determine expectation values and two-mode correlation functions of the expansion coefficients. The analytically solveable independent point-sources model is compared to an initial state model based on Glauber theory and two models based on the Color Glass Condensate framework. We find that the large wavelength modes of all investigated models show universal properties for central collisions and also discuss to which extent general properties of initial conditions can be understood analytically.