Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userLow-density in-medium effects on light clusters from heavy-ion data
67
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The modification of the ground state properties of light atomic nuclei in the nuclear and stellar medium is addressed, using chemical equilibrium constants evaluated from a new analysis of the intermediate energy heavy-ion (Xe$+$Sn) collision data measured by the INDRA collaboration. Three different reactions are considered, mainly differing by the isotopic content of the emission source. The thermodynamic conditions of the data samples are extracted from the measured multiplicities allowing for a parametrization of the in-medium modification, determined with the single hypothesis that the different nuclear species in a given sample correspond to a unique common value for the density of the expanding source. We show that this correction, which was not considered in previous analyses of chemical constants from heavy ion collisions, is necessary, since the observables of the analyzed systems show strong deviations from the expected results for an ideal gas of free clusters. This data set is further compared to a relativistic mean-field model, and seen to be reasonably compatible with a universal correction of the attractive $sigma$-meson coupling.
rate research
Read More
The equation of state with light clusters for nuclear and stellar matter is determined using chemical equilibrium constants evaluated from the analysis of the recently published (Xe$+$Sn) heavy ion data, corresponding to three reactions with different isotopic contents of the emission source. The measured multiplicities are used to extract the thermodynamic properties, and an in-medium correction to the ideal gas internal partition function of the clusters is included in the analysis. This in-medium correction and its respective uncertainty are calculated via a Bayesian analysis, with the unique hypothesis that the different nuclear species in a given sample must correspond to a unique common value for the density of the expanding source. Different parameter sets for the correction are tested, and the effect of the radius of the clusters on the thermodynamics and on the chemical equilibrium constants is also addressed. It is shown that the equilibrium constants obtained are almost independent of the isospin content of the analysed systems. Finally, a comparison with a relativistic mean field model proves that data are consistent with a universal in-medium correction of the scalar $sigma$-meson coupling for nucleons bound in clusters. The obtained value, $g_s/g_s^0 = 0.92 pm 0.02$, is larger than that obtained in a previous study not including in-medium effects in the data analysis. This result implies a smaller effect on the binding energy of the clusters and, as a consequence, larger melting densities, and an increased cluster contribution in supernova matter.
We report results of the first systematic simulation of proton and neutron density distributions in central heavy-ion collisions within the beam energy range of $ E_{rm beam} leq 800 , text{MeV/nucl}$ using pBUU and TDHF models. The symmetric $^text{40}$Ca +$^text{40}$Ca, $^text{48}$Ca +$^text{48}$Ca, $^text{100}$Sn +$^text{100}$Sn and $^text{120}$Sn + $^text{120}$Sn and asymmetric $^text{40}$Ca +$^text{48}$Ca and $^text{100}$Sn +$^text{120}$Sn systems were chosen for the simulations. We find limits on the maximum proton and neutron densities and the related proton-neutron asymmetry $delta$ as a function of the initial state, beam energy, system size and a symmetry energy model. While the maximum densities are almost independent of these parameters, our simulation reveals, for the first time, their subtle impact on the proton-neutron asymmetry. Most importantly, we find that variations in the proton-neutron asymmetry at maximum densities are related at most at 50% level to the details in the symmetry energy at supranormal density. The reminder is due to the details in the symmetry energy at subnormal densities and its impact on proton and neutron distributions in the initial state. This result puts to forefront the need of a proper initialization of the nuclei in the simulation, but also brings up the question of microscopy, such as shell effects, that affect initial proton and neutron densities, but cannot be consistently incorporated into semiclassical transport models.
We estimate the chemical freeze-out of light nuclear clusters for NICA energies of above 2 A GeV. On the one hand we use results from the low energy domain of about 35 A MeV, where medium effects have been shown to be important to explain experimental results. On the high energy side of LHC energies the statistical model without medium effects has provided results for the chemical freeze-out. The two approaches extrapolated to NICA energies show a discrepancy that can be attributed to medium effects and that for the deuteron/proton ratio amounts to a factor of about three. These findings underline the importance of a detailed investigation of light cluster production at NICA energies.
We present the transverse momentum spectra and rapidity distributions of $pi^{-}$ and K$^0_S$ in Ar+KCl reactions at a beam kinetic energy of 1.756 A GeV measured with the spectrometer HADES. The reconstructed K$^0_S$ sample is characterized by good event statistics for a wide range in momentum and rapidity. We compare the experimental $pi^{-}$ and K$^0_S$ distributions to predictions by the IQMD model. The model calculations show that K$^0_S$ at low tranverse momenta constitute a particularly well suited tool to investigate the kaon in-medium potential. Our K$^0_S$ data suggest a strong repulsive in-medium K$^0$ potential of about 40 MeV strength.
We study a problem of $pi$ production in heavy ion collisions in the context of the Isospin-dependent Boltzmann-Uehling-Uhlenbeck (IBUU) transport model. We generated nucleon densities using two different models, the Skyrme-Hartree-Fock (SHF) model and configuration interaction shell model (SM). Indeed, inter-nucleon correlations are explicitly taken into account in SM, while they are averaged in the SHF model. As an application of our theoretical frameworks, we calculated the $pi^{-}$ and $pi^{+}$ yields in collisions of nuclei with $A = 30-40$ nucleons. We used different harmonic oscillator lengths $b_{HO}$ to generate the harmonic oscillator basis for SM in order to study both theoretical and experimental cases. It is found that SM framework with $b_{HO}$ = 2.5 fm and SHF can be distinguished by the yield of $pi$ mesons, in this case the density distribution calculated by the shell model produces more $pi$ in the collision. In comparison, SM with $b_{HO}$ = 2.0 fm is characterized from SHF by the double $pi^{-}/pi^{+}$ ratios with different large impact parameters, from which one can find the double $pi^{-}/pi^{+}$ ratios of SM change smoother and are less than those of SHF.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
