Differential Neutron-Proton Squeeze-out

TL;DR

This paper proposes using the elliptic flow of neutrons and protons in relativistic heavy-ion collisions as a sensitive observable to probe the density dependence of the nuclear symmetry energy at high densities.

Contribution

It introduces the neutron-proton squeeze-out as a new observable for constraining the symmetry energy in nuclear matter at supra-normal densities.

Findings

Preliminary data favor a moderately soft symmetry term with gamma around 0.6.

The elliptic flow of neutrons and protons is sensitive to the symmetry energy.

Results suggest a specific density dependence of the symmetry potential.

Abstract

The elliptic flow (squeeze-out) of neutrons, protons and 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. Preliminary results from a study of the existing FOPI/LAND data for 197Au + 197Au collisions at 400 A MeV 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 = 0.6+-0.3.