arXiv subjects
Publications and source records attributed to Lie-Wen Chen.
We report recent results from a multiphase transport (AMPT) model on the azimuthal anisotropies of particle momentum distributions in heavy ion collisions at the Relativistic Heavy Ion Collider. These include higher-order anisotropic flows and their scaling, the rapidity dependence of anisotropic flows, and the elliptic flow of charm quarks.
Production of pentaquark $Θ^+$ baryons in central relativistic heavy ion collisions is studied in a kinetic model. Assuming that a quark-gluon plasma is produced in the collisions, we first determine the number of $Θ^+$ produced from the quark-gluon plasma using a parton coalescence model, and then take into consideration its production and absorption in subsequent hadronic matter via the reactions $KN\leftrightarrowΘ$, $KN\leftrightarrowπΘ$, and $\piN\leftrightarrow\bar KΘ$. We find that although the final $Θ^+$ number is affected by hadronic interactions, it remains sensitive to the initial number of $Θ^+$ produced from the quark-gluon plasma, particularly in the case of a small $Θ^+$ width as imposed by the $K^+N$ and $K^+d$ scattering data. Because of small baryon chemical potential in the hot dense matter produced in these collisions, the number of produced anti-$Θ$ is only slightly smaller than that of $Θ^+$.
Higher-order anisotropic flows $v_{4}$ and $v_{6}$ in heavy ion collisions at the Relativistic Heavy Ion Collider are studied in a multiphase transport model that has previously been used successfully for describing the elliptic flow $v_2$ in these collisions. We find that the same parton scattering cross section of about 10 \textrm{mb} used in explaining the measured $v_2$ can also reproduce the recent data on $v_{4}$ and $v_{6}$ from Au + Au collisions at $\sqrt{s}=200$ \textrm{AGeV}. It is further found that the $% v_{4}$ is a more sensitive probe of the initial partonic dynamics in these collisions than $v_{2}$. Moreover, higher-order parton anisotropic flows are nonnegligible and satisfy the scaling relation $v_{n,q}(p_{T})\sim v_{2,q}^{n/2}(p_{T})$, which leads naturally to the observed similar scaling relation among hadron anisotropic flows when the coalescence model is used to describe hadron production from the partonic matter.
Using an isospin- and momentum-dependent transport model, we study the effects due to the momentum dependence of isoscalar nuclear potential as well as that of symmetry potential on two-nucleon correlation functions and light cluster production in intermediate energy heavy-ion collisions induced by neutron-rich nuclei. It is found that both observables are affected significantly by the momentum dependence of nuclear potential, leading to a reduction of their sensitivity to the stiffness of nuclear symmetry energy. However, the t/$^{3}$He ratio remains a sensitive probe of the density dependence of nuclear symmetry energy.
Production of the doubly strange $Ξ$ baryon in heavy-ion collisions at \textrm{SIS} energies is studied in a relativistic transport model that includes perturbatively the strangeness-exchange reactions $\bar{K}Λ\to πΞ$ and $\bar{K}Σ\to πΞ$. Taking the cross sections for these reactions from the predictions of a hadronic model, we find that the $Ξ$ yield is about $10^{-4}$ in central collisions of $% ^{58}$Ni + $^{58}$Ni at $E/A=1.93$ \textrm{GeV}. The $Ξ$ yield is further found to be more sensitive to the magnitude of the cross sections for strangeness-exchange reactions than to the medium effects due to modified kaon properties. We have also made predictions for $Ξ$ production in Au+Au collisions at energies from 1 to 2 GeV/nucleon.
Based on the quark coalescence model, we derive relations among the momentum anisotropies of mesons and baryons in relativistic heavy ion collisions from a given, but arbitrary azimuthal distribution for the partons. Besides the familiar even Fourier coefficients such as the elliptic flow, we also pay attention to odd Fourier coefficients such as the directed flow, which has been observed at finite rapidity even at RHIC energies.
The coalescence model based on nucleon distribution functions from an isospin-dependent transport model is used to study the production of light clusters such as deuteron, triton, and $^{3}$He from heavy-ion collisions induced by neutron-rich nuclei at intermediate energies. It is found that the emission time of light clusters depends on their masses. For clusters with the same momentum per nucleon, heavier ones are emitted earlier. Both the yield and energy spectrum of light clusters are sensitive to the density dependence of nuclear symmetry energy, with more light clusters produced in the case of a stiff symmetry energy. On the other hand, effects due to the stiffness of the isoscalar part of nuclear equation of state and the medium dependence of nucleon-nucleon cross sections on light cluster production are unimportant. We have also studied the correlation functions of clusters, and they are affected by the density dependence of nuclear symmetry energy as well, with the stiff symmetry energy giving a stronger anti-correlation of light clusters, particularly for those with large kinetic energies. Dependence of light cluster production on the centrality and incident energy of heavy ion collisions as well as the mass of the reaction system is also investigated.
Using an isospin-dependent transport model, we study isospin effects on two-nucleon correlation functions in heavy-ion collisions induced by neutron-rich nuclei at intermediate energies. We find that these correlation functions are sensitive to the density dependence of nuclear symmetry energy, but not to the incompressibility of symmetric nuclear matter and the medium dependence of nucleon-nucleon cross sections. This sensitivity is mainly due to effects of nuclear symmetry energy on the emission times of neutrons and protons as well as their relative emission sequence. We also study the variations of the symmetry energy effects on nucleon-nucleon correlations with respect to the impact parameter, incident energy, and mass number of heavy ion collisions.
Using an isospin-dependent transport model for heavy-ion collisions induced by neutron-rich nuclei at intermediate energies, we study the production of light clusters such as deuteron, triton, and $^{3}$He via coalescence of nucleons. We find that both the yields and energy spectra of these light clusters are affected significantly by the density dependence of nuclear symmetry energy, with a stiffer symmetry energy giving a larger yield.
Using an isospin-dependent transport model, we study the effects of nuclear symmetry energy on two-nucleon correlation functions in heavy ion collisions induced by neutron-rich nuclei. We find that the density dependence of the nuclear symmetry energy affects significantly the nucleon emission times in these collisions, leading to larger values of two-nucleon correlation functions for a symmetry energy that has a stronger density dependence. Two-nucleon correlation functions are thus useful tools for extracting information about the nuclear symmetry energy from heavy ion collisions.
Within the framework of an isospin-dependent quantum molecular dynamics model, the zero-range 2-body part of the Skyrme interaction is replaced by a finite-range Gaussian 2-body interaction. From the transverse momentum analysis in the reaction of system $^{93}$Nb + $^{93}$Nb at energy of 400 MeV/nucleon and impact parameter $b$=3 fm, it is shown that the finite-range nuclear force enhances the transverse momentum of the reaction system and it can partly replace the momentum dependent part of the nucleon-nucleon interaction.
The squeeze-out flow in reactions of $^{124}$Sn + $^{124}$Sn and $^{124}$Ba + $^{124}$Ba at different incident energies for different impact parameters is investigated by means of an isospin-dependent quantum molecular dynamics model. For the first time, it is found that the more neutron-rich system ($% ^{124}$Sn + $^{124}$Sn) exhibits weaker squeeze-out flow. This isospin dependence of the squeeze-out flow is shown to mainly result from the isospin dependence of nucleon-nucleon cross section and the symmetry energy.
The proton fraction in ${\sl β}$-stable neutron stars is investigated within the framework of the Skyrme-Hartree-Fock theory using the extended Skyrme effective interaction for the first time. The calculated results show that the proton fraction disappears at high density, which implies that the pure neutron matter may exist in the interior of neutron stars. The incompressibility of the nuclear equation of state is shown to be more important to determine the proton fraction. Meanwhile, it is indicated that the addition of muons in neutron stars will change the proton fraction. It is also found that the higher-order terms of the nuclear symmetry energy have obvious effects on the proton fraction and the parabolic law of the nuclear symmetry energy is not enough to determine the proton fraction.
Within the framework of an isospin-dependent quantum molecular dynamics model, the rotational flow in reactions of $^{58}$Fe + $^{58}$Fe and $^{58}$% Ni + $^{58}$Ni at 40 MeV/nucleon for different impact parameters is investigated by analyzing the mid-rapidity azimuthal distribution. The rotational observables are also calculated semiquantitatively. For the first time, it is found that the more neutron-rich system ($^{58}$Fe + $^{58}$Fe) exhibits stronger rotational collective flow. This isospin dependence of rotational collective flow is more appreciable in semi-peripheral collisions and it is shown to mainly result from the isospin dependence of nucleon-nucleon cross section rather than the symmetry energy. Meanwhile, it is indicated that the rotational flow depends strongly on the impact parameter.