Constraints on models for the initial collision geometry in ultra relativistic heavy ion collisions

TL;DR

This paper uses Monte Carlo simulations to analyze how different initial collision geometries affect flow coefficients in heavy ion collisions, aiming to constrain models and improve viscosity measurements.

Contribution

It demonstrates that flow coefficient ratios can effectively distinguish between initial-state eccentricity models, reducing uncertainties in viscosity estimates.

Findings

Flow coefficient ratios vary significantly across models.

Measurements of $v_4/(v_2)^2$ can constrain initial geometry models.

Constraints improve the precision of viscosity determinations.

Abstract

Monte Carlo (MC) simulations are used to compute the centrality dependence of the collision zone eccentricities ($\epsilon_{2,4}$), for both spherical and deformed ground state nuclei, for different model scenarios. Sizable model dependent differences are observed. They indicate that measurements of the $2^{\text{nd}}$ and $4^{\text{th}}$ order Fourier flow coefficients $v_{2,4}$, expressed as the ratio $\frac{v_4}{(v_2)^2}$, can provide robust constraints for distinguishing between different theoretical models for the initial-state eccentricity. Such constraints could remove one of the largest impediments to a more precise determination of the specific viscosity from precision $v_{2,4}$ measurements at the Relativistic Heavy Ion Collider (RHIC).