Testing deconfinement at high isospin density

Abstract

We study the transition from hadronic matter to a mixed phase of quarks and hadrons at high baryon and isospin densities reached in heavy ion collisions. We focus our attention on the role played by the nucleon symmetry energy at high density.In this respect the inclusion of a scalar isovector meson, the \delta-coupling, in the Hadron Lagrangian appears rather important. We study in detail the formation of a drop of quark matter in the mixed phase, and we discuss the effects on the quark drop nucleation probability of the finite size and finite time duration of the high density region. We find that, if the parameters of quark models are fixed so that the existence of quark stars is allowed, then the density at which a mixed phase starts forming drops dramatically in the range Z/A \sim 0.3--0.4. This opens the possibility to verify the Witten-Bodmer hypothesis on absolute stability of quark matter using ground-based experiments in which neutron-rich nuclei are employed. These experiments can also provide rather stringent constraints on the Equation of State (EoS) to be used for describing the pre-Supernova gravitational collapse. Consistent simulations of neutron rich heavy ion collisions are performed in order to show that even at relatively low energies, in the few AGeV range, the system can enter such unstable mixed phase. Some precursor observables are suggested, in particular a ``neutron trapping'' effect

Symmetry energy softening in nuclear matter with non-nucleonic constituents

“…With increasing the isospin asymmetry, the critical density can be lowered rather dramatically. While the details of this issue with the MIT bag model can be found in the literature [25,34,35], we focus herein on the phase transition in symmetric matter where we indeed obtain the symmetry energy. It is however noteworthy to point out that the softening of the symmetry energy can play a moderate role in increasing the critical density in asymmetric matter, with the magnitude depending on the bag constant.…”

“…Most likely, the high-density symmetry energy extracted from the heavy-ion collisions would be as soft as that presented in this work as long as a detailed discrimination or calibration is not ready for dynamically evolutional matter. In deed, the extraction of the symmetry energy encounters the finite size effects which can cause the increase of the critical density [25]. However, the decreasing tendency of the nuclear symmetry energy above the critical density will not be altered by the finite size effects.…”

“…Nuclear matter at this density domain can be produced via heavy-ion collisions, and it usually includes the admixture of non-nucleonic degrees of freedom. In the past, the symmetry energy effects on these phase transitions have been found to be very significant [23,25,26]. However, the effects of new constituents on the symmetry energy are seldom investigated.…”

Influence of vector interactions on the hadron-quark/gluon phase transition

“…Recently, the two-phase model with both hadron and quark degrees of freedom, widely used in the description of the phase transition in neutron star matter under the weak equilibrium (e.g., [36][37][38][39][40][41][42][43][44][45] ), has also been taken to study the phase transition related to heavy-ion collisions [46][47][48][49][50][51][52][53][54], particularly the phase transition in asymmetric matter. The latter is possible to be probed in the planned facilities, such as FAIR at GSI-Darmstadt and NICA at JINR-Dubna [47,[49][50][51][52][53][54]. In these studies, only the scalar interacting channel was considered for quark matter, and this channel interaction is responsible for the dynamical masses of quarks.…”

Hot and dense nuclear matter in an extended mean field approach

“…All the thermodynamical quantities can be obtained from the baryon grand potential Ω B in the standard way [4]. At low baryon density and high temperature, the contribution of the lightest pseudoscalar and vector mesons to the total thermodynamical potential becomes very relevant.…”