Kaon Production In Heavy-ion Collisions Research Articles

Systematics on the high-density nuclear equation of state from relativistic Hartree-Fock theory with Brown-Rho scaling

Using the Brown-Rho (BR) scaling law, several new relativistic Hartree-Fock (RHF) models with chiral limit are thoroughly investigated. The high-density nuclear equation of state (EOS) of RHF with the BR scaling become softer than one without the BR scaling. The EOS of RHF with BR scaling is consistent with the constraint extracted from collective flows and kaon production in heavy-ion collisions. It is found that, with a sizable strength parameter of the mass drop $x=0.126$, the symmetry energy is almost flat at density above 3 times the saturation density ${\ensuremath{\rho}}_{0}$, and even decreases slightly. This is caused from the fact that the decline of the potential part of symmetry energy is faster than the increase of the kinetic part of symmetry energy. The decrease of potential part is mainly because the neutron mass ${M}_{n}^{*}$ and the proton mass ${M}_{p}^{*}$ are close to each other when the density gradually approaches the critical density of chiral limit. For a mass drop of $x=0.092$, since the critical density of chiral limit is higher than one of $x=0.126$, the symmetry energy becomes flat at density above $5{\ensuremath{\rho}}_{0}$. While, since the critical density of chiral limit is very high for a small mass drop $x=0.053$, the symmetry energy of RHFs with $x=0.053$ always increases at the entire density domain of this work (below 6 ${\ensuremath{\rho}}_{0}$). The maximum mass of neutron star (NS) obtained with present models can satisfy $M=2.08\ifmmode\pm\else\textpm\fi{}0.07{M}_{\ensuremath{\bigodot}}$. However, the radius of 1.4 ${M}_{\ensuremath{\bigodot}}$ with the mass drop of $x=0.126$ will surpass the upper limit (13.7 km) extracted from the tidal deformability parameter of coalescence of a NS binary system and the radius of $\text{J0030}+0451$ being $12.{71}_{\ensuremath{-}1.19}^{+1.14}$ km. The radius of 1.4 ${M}_{\ensuremath{\bigodot}}$ with the mass drop of $x=0.092$ is 13.6 km, closing to 13.7 km and the radius of $\text{J0030}+0451$ being $12.{71}_{\ensuremath{-}1.19}^{+1.14}$ km. Therefore, the RHF model with BR scaling prefers the mass drop of $x\ensuremath{\lesssim}0.092$.

Nuclear in-medium and isospin effects on subthreshold kaon production in heavy-ion collisions

Subthreshold kaon (K$^{0}$ and K$^{+}$) production in neutron-rich nuclear reactions to probe the kaon-nucleon interaction in nuclear medium and to extract the isospin dependent part of the nuclear equation of state at high-baryon densities, is investigated within an isospin and momentum dependent transport model. A repulsive kaon-nucleon potential is implemented in the model through fitting the flow data and inclusive spectra in heavy-ion collisions, which enhances the energetic kaon emission squeezed out in the reaction zone and leads to a variation of the high-momentum spectrum of the K$^{0}$/K$^{+}$ yields. It is found that the stiffness of nuclear symmetry energy plays a significant role on the isospin ratio with decreasing the incident energy and a hard symmetry energy has a larger value of the K$^{0}$/K$^{+}$ ratio in the domain of subthreshold energies.

Strangeness in astrophysics and cosmology

Some recent developments concerning the role of strange quark matter for astrophysical systems and the QCD phase transition in the early universe are addressed. Causality constraints of the soft nuclear equation of state as extracted from subthreshold kaon production in heavy-ion collisions are used to derive an upper mass limit for compact stars. The interplay between the viscosity of strange quark matter and the gravitational wave emission from rotation-powered pulsars are outlined. The flux of strange quark matter nuggets in cosmic rays is put into perspective with a detailed numerical investigation of the merger of two strange stars. Finally, we discuss a novel scenario for the QCD phase transition in the early universe, which allows for a small inflationary period due to a pronounced first-order phase transition at large baryochemical potential.

Strangeness in Compact Stars

We discuss the impact of strange hadrons, in particular hyperons, on the gross features of compact stars and on core-collapse supernovae. Hyperons are likely to be the first exotic species which appears around twice normal nuclear matter density in the core of neutron stars. Their presence largely influences the mass-radius relation of compact stars, the maximum mass, the cooling of neutron stars, the stability with regard to the emission of gravitational waves from rotation-powered neutron stars and the possible early onset of the QCD phase transition in core-collapse supernovae. We outline also the constraints from subthreshold kaon production in heavy-ion collisions for the maximum possible mass of neutron stars.

Evidence for a Soft Nuclear Equation-of-State from Kaon Production in Heavy-Ion Collisions.

The production of pions and kaons has been measured in 197Au+197Au collisions at beam energies from 0.6 to 1.5A GeV with the kaon spectrometer at SIS/GSI. The K+ meson multiplicity per nucleon is enhanced in Au+Au collisions by factors up to 6 relative to C+C reactions, whereas the corresponding pion ratio is reduced. The ratio of the K+ meson excitation functions for Au+Au and C+C collisions increases with decreasing beam energy. This behavior is expected for a soft nuclear equation-of-state.

Kaon production in heavy-ion collisions and kaon condensation in neutron stars

The recent past witnesses the growing interdependence between the physics of hadrons, the physics of relativistic heavy-ion collisions, and the physics of compact objects in astrophysics. A notable example is the kaon which plays a special roles in all the three fields. In this contribution, we present a transport model study of kaon production and flow in heavy-ion collisions at SIS energies. We also discuss the effects of the kaon in-medium properties extracted from heavy-ion data on neutron star properties.

Resonance model study of kaon production in baryon-baryon reactions for heavy-ion collisions

The energy dependence of the total kaon production cross sections in baryon-baryon (N and {Delta}) collisions are studied in the resonance model, which is a relativistic tree-level treatment. This study is the first attempt to complete a systematic consistent investigation of the elementary kaon production reactions for both the pion-baryon and baryon-baryon reactions. Our model suggests that the magnitudes of the isospin-averaged total cross sections for the NN{r_arrow}NYK and {Delta}N{r_arrow}NYK (Y={Lambda} or {Sigma}) reactions are almost equal at energies up to about 200 MeV above threshold. However, the magnitudes for the {Delta}N reactions become about 6 times larger than those for the NN reactions at energies about 1 GeV above threshold. Furthermore, the magnitudes of the isospin-averaged total cross sections for the NN{r_arrow}{Delta}YK reactions turn out to be comparable to those for the NN{r_arrow}NYK reactions at NN invariant collision energies about 3.1 GeV, and about 5 to 10 times larger at NN invariant collision energies about 3.5 GeV. The microscopic cross sections are parametrized in all isospin channels necessary for the transport model studies of kaon production in heavy-ion collisions. These cross sections are then applied in the relativistic transport model to study the sensitivity to the underlying elementary kaonmore » production cross sections. {copyright} {ital 1999} {ital The American Physical Society}« less

Comment on “Kaon Production in Heavy-Ion Collisions and Maximum Mass of Neutron Stars”

A Comment on the Letter by G. Q. Li, C.-H. Lee, and G. E. Brown, Phys. Rev. Lett. 79, 5214 (1997). The authors of the Letter offer a Reply.

Kaon Production in Heavy-Ion Collisions and Maximum Mass of Neutron Stars

We determine an ``empirical'' kaon dispersion relation by analyzing and fitting recent experimental data on kaon production in heavy-ion collisions. We then investigate its effects on the hadronic equation of state at high densities and on neutron star properties. We find that the maximum mass of neutron stars can be lowered by about ${0.4M}_{\ensuremath{\bigodot}}$ once kaon condensation as constrained by our empirical dispersion relation is introduced. We emphasize the growing interplay between hadron physics, relativistic heavy-ion physics, and the physics of compact objects in astrophysics.

Kaons in dense matter, kaon production in heavy-ion collisions, and kaon condensation in neutron stars

The recent past witnesses the growing interdependence between the physics of hadrons, the physics of relativistic heavy-ion collisions, and the physics of compact objects in astrophysics. A notable example is the kaon which plays special roles in all the three fields. In this paper, we first review the various theoretical investigations of kaon properties in nuclear medium, focusing on possible uncertainties in each model. We then present a detailed transport model study of kaon production in heavy-ion collisions at SIS energies. We shall discuss especially the elementary kaon and antikaon production cross sections in hadron-hadron interactions, that represent one of the most serious uncertainties in the transport model study of particle production in heavy-ion collisions. The main purpose of such a study is to constrain kaon in-medium properties from the heavy-ion data. This can provide useful guidances for the development of theoretical models of the kaon in medium. In the last part of the paper, we apply the kaon in-medium properties extracted from heavy-ion data to the study of neutron star properties. Based on a conventional equation of state of nuclear matter that can be considered as one of the best constrained by available experimental data on finite nuclei, we find that the maximum mass of neutron stars is about 2 M ⊙, which is reduced to about 1.5 M ⊙ once kaon condensation as constrained by heavy-ion data is introduced.

Resonance model of pi Delta to YK for kaon production in heavy-ion collisions

The elementary production cross sections pi Delta to YK (Y= Sigma , Lambda ) and pi N to YK are needed to describe kaon production in heavy-ion collisions. The pi N to YK reactions were studied previously by a resonance model. The model can explain quite well the experimental data obtained by us. In this article, the total cross sections pi Delta to YK at intermediate energies (from the kaon production threshold to 3 GeV of pi Delta centre-of-mass energy) are calculated for the first time using the same resonance model. The resonances, N(1710)I(JP)= 1/2 ( 1/2 +) and N(1720) 1/2 (3/2+) for the pi Delta to Sigma K reactions, and N(1650) 1/2 ( 1/2 -) N(1710) 1/2 ( 1/2 +) and N(1720) 1/2 (3/2+) for the pi Delta to Lambda K reactions are taken into account coherently as the intermediate states in the calculations. Also, t-channel K*(892) 1/2 (1-) vector-meson exchange is included. The results show that K*(892) exchange is negligible for the pi Delta to Sigma K reactions, whereas this meson does not contribute to the pi Delta to Lambda K reactions. Furthermore, the pi Delta to YK contributions to kaon production in heavy-ion collisions are not only non-negligible but also very different from the pi N to YK reactions. An argument valid for pi N to YK cannot be extended to pi Delta to YK reactions. Therefore, cross sections for pi Delta to YK correctly including the different isospins must be calculated for inclusion in simulation codes for kaon production in heavy-ion collisions, where no experimental data are available. Parametrizations of the total cross sections pi Delta to YK for kaon production in heavy-ion collisions are given based on this work.

The relativistic transport model description of subthreshold kaon production in heavy-ion collisions

The relativistic transport model, in which the nucleon effective mass is connected to the scalar field while its energy is shifted by the vector potential, is extended to include the kaon degree of freedom. We further take into account the medium modification of the kaon mass due to explicit chiral symmetry breaking. Both the propagation of kaons in the mean-field potential and the kaon-baryon elastic scattering are explicitly treated in our study. We find that the attractive kaon scalar mean-field potential in the dense matter leads to an enhanced kaon yield in heavy-ion collisions at energies of about 1 GeV/nucleon that are below the threshold for kaon production from the nucleon-nucleon interaction in free space. The final-state kaon-baryon scattering is seen to affect significantly the kaon momentum spectra, leading to an enhanced yield of kaons with large momenta or at large laboratory angles. With a soft nuclear equation of state and including the attractive kaon scalar potential, the calculated kaon energy spectra agree with the preliminary data on subthreshold kaon production from the heavy-ion synchrotron at GSI.

Medium effects on subthreshold kaon production in heavy-ion collisions.

The relativistic transport model is extended to include the kaon degree of freedom. We also take into account the density dependence of the kaon effective mass in nuclear matter and the rescattering of kaons by nucleons. We find that the inclusion of kaon self-energy due to the attractive scalar mean field leads to an enhanced kaon yield in heavy-ion collisions at subthreshold energies. Also, kaon rescatterings are found to affect significantly the final kaon momentum spectra. We compare the theoretical results with recent experimental data from the Heavy-Ion Synchrotron (SIS) at GSI.

The Boltzmann-Langevin model for nuclear collisions

An extension of the one-body transport models is developed by incorporating correlations into the equation of motion in a stochastic approximation. In the semiclassical limit, this yields the Boltzmann-Langevin Equation for the fluctuating single-particle density in the phase-space. In order to investigate the gross-properties of density fluctuations in heavy-ion collisions, a number of calculations have been carried out. These calculations reveal that large dynamical fluctuations are introduced into the momentum space during the early stages of the collision, which cause the nuclear system to decay into a great variety of final channels. The effects of the fluctuations on the kaon production in heavy-ion collisions at sub-threshold energies are also investigated.