Spinodal Instability at the Onset of Collective Expansion in Nuclear Collisions

TL;DR

This paper predicts observable spinodal instability effects during the onset of collective expansion in nuclear collisions, using transport models to identify transient ring structures in collision remnants.

Contribution

It introduces the first clear prediction of spinodal instability effects in nuclear collisions using two different transport models.

Findings

Transient ring structures formed by projectile and target remnants.

Spinodal instability influences the formation of observable ring patterns.

Predicted structures could be detected in experimental flow data.

Abstract

Using transport theory to model central Au + Au collisions in the energy region of 20 - 110 MeV/u, at impact parameters b <= 5 fm, we predict a measurable impact of spinoidal instability as the collective expansion sets in with energy. Two transport models are employed, the pBUU model, solving a Boltzmann-Uehling-Uhlenbeck equation, and the Brownian Motion (BM) model, solving a set of Langevin equations to describe the motion of individual nucleons in a noisy nuclear medium. We find without ambiguity, for the first time, that a combination of delayed equilibration, onset of collective expansion and the spinodal instability produces a pair of transient ring structures, made of the projectile and target remnants, with spectator nucleons predicted to end in the entities reminiscent of stones in jewelry, on the rings. The ring structures, calculated in the configuration space and mapped onto the velocity space, could be detected in experimental collective flow data.