Progress in constraining the asymmetry dependence of the nuclear caloric curve

Abstract

The nuclear equation of state is a basic emergent property of nuclear material. Despite its importance in nuclear physics and astrophysics, aspects of it are still poorly constrained. Our research focuses on answering the question: How does the nuclear caloric curve depend on the neutron-proton asymmetry? We briefly describe our initial observation that increasing neutron-richness leads to lower temperatures. We then discuss the status of our recently executed experiment to independently measure the asymmetry dependence of the caloric curve.The nuclear equation of state (EOS) relates the thermodynamic state variables temperature, pressure, density, internal energy, and neutronproton asymmetry. It describes the evolution of finite excited nuclear systems created in terrestrial accelerator experiments and finds application in many aspects of nuclear astrophysics as well. Our knowledge of the EOS is well constrained for nuclear systems near beta stability. However, extrapolation to very exotic environments far from beta stability (e.g. neutron stars) represents the largest uncertainty in the EOS. We approach this deficiency in a unique way by seeking to answer the question: How does the caloric curve depend on the neutron-proton asymmetry?To date, the theoretical approaches [1][2][3][4][5][6] that have been applied to this question have provided answers that differ not only in magnitude but in sign: some predict a decrease in temperature with increasing neutron content, while others predict just the opposite. This discrepancy stems in part 201 , 0 0 EPJ Web of Conferences

Constraints on the asymmetric equation of state from heavy-ion collisions

“…[11] In order to extract a meaningful value of symmetry energy from isoscaling one must accurately know the (N − Z)/A of the sources and the temperature of the system. Recent work by McIntosh [12][13][14][15] has demonstrated that there is an (N − Z)/A dependence in the nuclear caloric curve. One also must take into account any secondary cooling or experimental filters that are needed to map the observed fragments to primary fragments.…”