The Symmetry Energy of the Nuclear EoS: A Study of Collective Motion and Low-Energy Reaction Dynamics in Semiclassical Approaches

Stefano Burrello,Hua Zheng,Maria Colonna

doi:10.3389/fphy.2019.00053

Abstract

In the framework of mean-field based transport approaches, we discuss recent results concerning collective motion and low-energy heavy ion reactions involving neutron-rich systems. We focus on aspects which are particularly sensitive to the isovector terms of the nuclear effective interaction and the corresponding symmetry energy. As far as collective excitations are concerned, we discuss the mixed nature of dipole oscillations in neutron-rich systems. On the other hand, for reactions close to the Coulomb barrier, we investigate the structure of pre-equilibrium collective dipole oscillations, focusing on their sensitivity to the symmetry energy behavior below normal density. Nucleon emission is also considered within the same context. The possible impact of other relevant terms of the nuclear effective interaction on these mechanisms is also examined. From this analysis we expect to put further constraints on the nuclear Equation of State, of crucial importance also in the astrophysical context.

Highlights

Collective patterns exhibited by complex systems can bear important information on relevant properties of the particle interaction
These low-lying excitations, which are referred in the literature as Pygmy Dipole Resonance (PDR), have been the object of intense discussion [12,13,14,15,16,17,18,19,20,21,22,23], proving to be, like the giant dipole resonance (GDR), an important probe of crucial information of the nuclear effective interaction, especially concerning its isovector component and the corresponding contribution to the Equation of State (EoS) [24,25,26], namely the symmetry energy
In this article we review recent studies devoted to the investigation, within a semi-classical transport approach, of collective excitations in isolated nuclei and of pre-equilibrium effects, such as dipole radiation and nucleon emission, occurring in nuclear reactions at low beam energy [39, 40]

Summary

Introduction

Collective patterns exhibited by complex systems can bear important information on relevant properties of the particle interaction. In the case of nuclei with some neutron excess, a strong fragmentation of strength has been observed in the isovector dipole response, mainly located at lower energy with respect to the GDR [2,3,4,5,6,7,8,9,10,11] These low-lying excitations, which are referred in the literature as Pygmy Dipole Resonance (PDR), have been the object of intense discussion [12,13,14,15,16,17,18,19,20,21,22,23], proving to be, like the GDR, an important probe of crucial information of the nuclear effective interaction, especially concerning its isovector component and the corresponding contribution to the Equation of State (EoS) [24,25,26], namely the symmetry energy

Objectives

Results

Conclusion