The LIGO-Virgo collaboration detection of the binary neutron-star merger event, GW170817, has expanded efforts to understand the Equation of State (EoS) of nuclear matter. These measurements provide ...new constraints on the overall pressure, but do not elucidate its origins, by not distinguishing the contribution to the pressure from symmetry energy which governs much of the internal structure of a neutron star. By combining the neutron star EoS extracted from the GW170817 event and the EoS of symmetric matter from nucleus-nucleus collision experiments, we extract the symmetry pressure, which is the difference in pressure between neutron and nuclear matter over the density region from 1.2ρ0 to 4.5ρ0. While the uncertainties in the symmetry pressure are large, they can be reduced with new experimental and astrophysical results.
Collisions involving 112Sn and 124Sn nuclei have been simulated with the improved quantum molecular dynamics transport model. The results of the calculations reproduce isospin diffusion data from two ...different observables and the ratios of neutron and proton spectra. By comparing these data to calculations performed over a range of symmetry energies at saturation density and different representations of the density dependence of the symmetry energy, constraints on the density dependence of the symmetry energy at subnormal density are obtained. The results from the present work are compared to constraints put forward in other recent analyses.
We systematically explore the relative impact of the Coulomb interaction and the nuclear symmetry energy on the proton and neutron density distributions in the 212Pb + 208Pb, 132Sn + 124Sn and 54Ca + ...48Ca central collisions at beam energies below 800 MeV/A. The Boltzmann-Uhlenbeck-Uehling (pBUU) transport and the Time-Dependent-Hartree-Fock (TDHF) frameworks with SV-bas and SV-sym34 Skyrme parametrizations are employed. Maximum total particle number density and the proton-neutron (isospin) asymmetry have been calculated as a function of beam energy, system size and the Skyrme model, with and without the Coulomb force for all systems. The maximum total density, overall not exceeding 2.5-3.0ρ0 (ρ0=0.16fm−3), is observed to be lowered by the Coulomb interaction by less than 10%. The maximal asymmetries are not enhanced but decreased in the reaction as compared to the initial state in the majority of cases, and lowered by up to 45% due to the Coulomb effects. Furthermore, the proton and neutron density distributions in the plane transverse to the beam direction have been modelled. The distributions are found to vary throughout the reaction space, with the Coulomb force increasing the isospin differences closer to the center of the collision. The general conclusion of this work is that the Coulomb interaction plays a significant role in the collision dynamics, and enhances the rather weak response of the colliding systems to the nuclear symmetry energy and its density dependence. Thus, inferring symmetry energy from comparing theory and data requires careful modelling of Coulomb effects, in addition to nuclear, in any reaction simulation.
The shear viscosity to entropy ratio (eta/s) is estimated for the hot and dense QCD matter created in Au+Au collisions at BNL Relativistic Heavy Ion Collider (square roots_{NN}=200 GeV). A very low ...value is found; eta/s approximately 0.1, which is close to the conjectured lower bound (1/4pi). It is argued that such a low value is indicative of thermodynamic trajectories for the decaying matter which lie close to the QCD critical end point.
The emissions of neutrons, protons and bound clusters from central 124Sn+124Sn and 112Sn+112Sn collisions are simulated using the Improved Quantum Molecular Dynamics model for two different ...density-dependent symmetry-energy functions. The calculated neutron–proton spectral double ratios for these two systems are sensitive to the density dependence of the symmetry energy, consistent with previous work. Cluster emission increases the double ratios in the low energy region relative to values calculated in a coalescence-invariant approach. To circumvent uncertainties in cluster production and secondary decays, it is important to have more accurate measurements of the neutron–proton ratios at higher energies in the center of mass system, where the influence of such effects is reduced.
Using symmetric 112Sn+112Sn, 124Sn+124Sn collisions as references, we probe isospin diffusion in peripheral asymmetric 112Sn+124Sn, 124Sn+112Sn systems at an incident energy of E/A=50 MeV. Isoscaling ...analyses imply that the quasiprojectile and quasitarget in these collisions do not achieve isospin equilibrium, permitting an assessment of isospin transport rates. We find that comparisons between isospin sensitive experimental and theoretical observables, using suitably chosen scaled ratios, permit investigation of the density dependence of the asymmetry term of the nuclear equation of state.
Light cluster production at NICA Bastian, N. -U.; Batyuk, P.; Blaschke, D. ...
The European physical journal. A, Hadrons and nuclei,
08/2016, Letnik:
52, Številka:
8
Journal Article
Recenzirano
Odprti dostop
.
Light cluster production at the NICA accelerator complex offers unique possibilities to use these states as “rare probes” of in-medium characteristics such as phase space occupation and early flow. ...In order to explain this statement, in this contribution theoretical considerations from the nuclear statistical equilibrium model and from a quantum statistical model of cluster production are supplemented with a discussion of a transport model for light cluster formation and with results from hydrodynamic simulations combined with the coalescence model.
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