Dynamical and statistical bimodality in nuclear fragmentation

TL;DR

This paper reexamines bimodal behavior in nuclear fragmentation using simulations, showing it can arise from both dynamical fluctuations and thermal phase transitions, depending on reaction conditions.

Contribution

It demonstrates that bimodality in heavy ion reactions results from both entrance and exit channel effects, unifying previously conflicting interpretations.

Findings

Bimodality can originate from fluctuations in collision rates.

Thermal bimodality linked to nuclear liquid-gas phase transition is observed.

Heavy ion collisions serve as a tool to study critical phenomena and phase transitions.

Abstract

The origin of bimodal behavior in the residue distribution experimentally measured in heavy ion reactions is reexamined using Boltzmann-Uehling-Uhlenbeck simulations. We suggest that, depending on the incident energy and impact parameter of the reaction, both entrance channel and exit channel effects can be at the origin of the observed behavior. Specifically, fluctuations in the reaction mechanism induced by fluctuations in the collision rate, as well as thermal bimodality directly linked to the nuclear liquid-gas phase transition are observed in our simulations. Both phenomenologies were previously proposed in the literature, but presented as incompatible and contradictory interpretations of the experimental measurements. These results indicate that heavy ion collisions at intermediate energies can be viewed as a powerful tool to study both bifurcations induced by out-of-equilibrium critical phenomena, as well as finite size precursors of thermal phase transitions.