Symmetry energy from elliptic flow in 197Au + 197Au

TL;DR

This paper investigates the symmetry energy in nuclear matter by analyzing elliptic flow data from gold-gold collisions, suggesting a moderately soft symmetry term at high densities.

Contribution

It introduces the elliptic-flow ratio as a new observable to probe the symmetry energy at supra-normal densities in heavy-ion collisions.

Findings

Favoring a moderately soft symmetry term with gamma ≈ 0.9

Data supports a specific density dependence of the symmetry potential

Provides constraints on the equation of state at high densities

Abstract

The elliptic-flow ratio of neutrons with respect to protons or light complex particles in reactions of neutron-rich systems at relativistic energies is proposed as an observable sensitive to the strength of the symmetry term in the equation of state at supra-normal densities. The results obtained from the existing FOPI/LAND data for 197Au + 197Au collisions at 400 MeV/nucleon in comparison with the UrQMD model favor a moderately soft symmetry term with a density dependence of the potential term proportional to rho/rho_0^gamma with gamma = 0.9 +- 0.4.