On the Origin of the Elliptic Flow and its Dependence on the Equation of State in Heavy Ion Reactions at Intermediate Energies

TL;DR

This paper investigates the origin of elliptic flow in heavy-ion collisions at intermediate energies, showing its strong dependence on the nuclear equation of state and explaining the underlying physical mechanisms through quantum molecular dynamics simulations.

Contribution

It demonstrates that the elliptic flow's sensitivity to the nuclear EoS arises from density gradients influenced by spectator matter, supported by QMD model calculations.

Findings

Elliptic flow v2 is highly sensitive to the nuclear EoS.

Density gradients in the reaction plane influence particle acceleration.

Soft momentum-dependent EoS reproduces experimental data.

Abstract

Recently it has been discovered that the elliptic flow, v2, of composite charged particles emitted at midrapidity in Heavy-Ion collisions at intermediate energies shows the strongest sensitivity to the Nuclear Equation of State (EoS) which has been observed up to now within a microscopic model. This dependence on the nuclear EoS is predicted by Quantum Molecular Dynamics (QMD) calculations [1] which show as well that the absorption or rescattering of in-plane emitted particles by the spectator matter is not the main reason for the EoS dependence of the elliptic flow at mid-rapidity but different density gradients (and therefore different forces) in the direction of the impact parameter (x-direction) as compared to the direction perpendicular to the reaction plan (y-direction), caused by the presence of the spectator matter. The stronger density gradient in y-direction accelerates the particles more and creates therefore a negative v2. When using a soft momentum dependent EoS, the QMD calculations reproduce the experimental results.