arXiv subjects

Che Ming Ko

Publications and source records attributed to Che Ming Ko.

At least 163 records · Page 9Linked to original sources

arXiv2004

Determination of the stiffness of the nuclear symmetry energy from isospin diffusion

With an isospin- and momentum-dependent transport model, we find that the degree of isospin diffusion in heavy ion collisions at intermediate energies is affected by both the stiffness of the nuclear symmetry energy and the momentum dependence of the nucleon potential. Using a momentum dependence derived from the Gogny effective interaction, recent experimental data from NSCL/MSU on isospin diffusion are shown to be consistent with a nuclear symmetry energy given by $E_{\text{sym}}(ρ)\approx 31.6(ρ/ρ_{0})^{1.05} $ at subnormal densities. This leads to a significantly constrained value of about -550 MeV for the isospin-dependent part of the isobaric incompressibility of isospin asymmetric nuclear matter.

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arXiv2004

Pseudorapidity dependence of anisotropic flows in relativistic heavy-ion collisions

The pseudorapidity dependence of anisotropic flows $v_{1}$, $v_{2}$, $v_{3}$ , and $v_{4}$ of charged hadrons in heavy-ion collisions at the Relativistic Heavy Ion Collider is studied in a multi-phase transport model. We find that while the string melting scenario, in which hadrons that are expected to be formed from initial strings are converted to their valence quarks and antiquarks, can explain the measured $p_{T}$-dependence of $v_{2}$ and $ v_{4} $ of charged hadrons at midrapidity with a parton scattering cross section of about 10 \textrm{mb}, the scenario without string melting reproduces better the recent data on $v_{1}$ and $v_{2}$ of charged hadrons at large pseudorapidity in Au + Au collisions at $\sqrt{s}=200$ AGeV . Our results thus suggest that a partonic matter is formed during early stage of relativistic heavy ion collisions only around midrapidity and that strings remain dominant at large rapidities. The $p_{T}$-dependence of $v_{1} $, $v_{2}$, $v_{3}$ and $v_{4}$ for charged hadrons at forward pseudorapidity is also predicted, and we find that while $v_{1}$ and $v_{2}$ are appreciable at large pseudorapidity the higher-order anisotropic flows $v_{3}$ and $v_{4} $ are essentially zero.

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arXiv2004

Partonic effects on anisotropic flows at RHIC

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.

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arXiv2004

Cascade production in heavy-ion collisions at SIS energies

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.

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arXiv2004

Momentum anisotropies in the quark coalescence model

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.

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arXiv2003

Deuteron-Nucleus Collisions in a Multi-Phase Transport Model

Using a multi-phase transport (AMPT) model, we study pseudo-rapidity distributions and transverse momentum spectra in deuteron-gold collisions at RHIC. We find that final-state partonic and hadronic interactions affect the transverse momentum spectrum of protons more than those of kaons or pions. Relative to p+p collisions at same center-of-mass energy per nucleon pair, the effect of final-state interactions on the charged particle transverse momentum spectra in d+Au collisions is much smaller than observed in experimental data, indicating that initial-state effects such as the Cronin effect are important.

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arXiv2003

Charm production from proton-proton collisions

We evaluate the cross sections for charmed hadron production from proton-proton reactions $pp\to\bar D^0pΛ_c^+$ and $pp\to\bar D^{*0}pΛ_c^+$ using a hadronic Lagrangian. With empirical coupling constants and cutoff parameters in the form factors, sum of their cross sections at center-of-mass energy of 11.5 GeV is about 1 $μ$b and is comparable to measured inclusive cross section for charmed hadron production from proton-proton reactions. The cross section decreases to about 1 nb at 40 MeV above threshold.

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arXiv2003

Light clusters production as a probe to the nuclear symmetry energy

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.

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arXiv2003

Effect of symmetry energy on two-nucleon correlation functions in heavy-ion collisions induced by neutron-rich nuclei

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.

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arXiv2003

Charm production from photo-nucleon reaction in a hadronic model

We study the total cross section for photo production of open charm hadrons near threshold using a hadronic Lagrangian. Both two-body final states involving $Λ_c$ and a charmed meson as well as three-body final states involving nucleon and a charm-anticharm meson pair are included. With appropriate cut-off parameters in the form factors at interaction vertices, the model gives a total cross section that is consistent with the measured data at center-of-mass energy of 6 GeV. The result is compared with the prediction from the leading-order perturbative QCD.

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arXiv1999

A transport model for heavy ion collisions at RHIC

To study heavy ion collisions at energies to be available from the Relativistic Heavy Ion Collider (RHIC), we have developed a transport model that includes both initial partonic and final hadronic interactions. Specifically, the parton cascade model ZPC, which uses as input the parton distribution from the HIJING model, is extended to include the quark-gluon to hadronic matter transition and also final-state hadronic interactions based on the ART model. Comparisons with SPS data and predictions for RHIC are reported.

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arXiv1999

Elliptic flow from a parton cascade

The dependence of elliptic flow at RHIC energies on the effective parton scattering cross section is calculated using the ZPC parton cascade model. We show that the v_2 measure of elliptic flow saturates early in the evolution before the hadronization transition to a rather large value ~0.05-0.15 as σ_g varies from 2-10 mb and thus is a sensitive probe of the dynamics in the plasma phase.

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arXiv1997

Isospin Physics in Heavy-Ion Collisions at Intermediate Energies

In nuclear collisions induced by stable or radioactive neutron-rich nuclei a transient state of nuclear matter with an appreciable isospin asymmetry as well as thermal and compressional excitation can be created. This offers the possibility to study the properties of nuclear matter in the region between symmetric nuclear matter and pure neutron matter. In this review, we discuss recent theoretical studies of the equation of state of isospin-asymmetric nuclear matter and its relations to the properties of neutron stars and radioactive nuclei. Chemical and mechanical instabilities as well as the liquid-gas phase transition in asymmetric nuclear matter are investigated. The in-medium nucleon-nucleon cross sections at different isospin states are reviewed as they affect significantly the dynamics of heavy ion collisions induced by radioactive beams. We then discuss an isospin-dependent transport model, which includes different mean-field potentials and cross sections for the proton and neutron, and its application to these reactions. Furthermore, we review the comparisons between theoretical predictions and available experimental data. In particular, we discuss the study of nuclear stopping in terms of isospin equilibration, the dependence of nuclear collective flow and balance energy on the isospin-dependent nuclear equation of state and cross sections, the isospin dependence of total nuclear reaction cross sections, and the role of isospin in preequilibrium nucleon emissions and subthreshold pion production.

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arXiv1996

Kaon dispersion relation and flow in relativistic heavy-ion collisions

Within the framework of a relativistic transport model (ART) for heavy-ion collisions at AGS energies, we examine the effects of kaon dispersion relation on the transverse flow of kaons and their transverse momentum and azimuthal angle distributions. We find that the transverse flow is the most sensitive observable for studying the kaon dispersion relation in dense medium.

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arXiv1996

Pion Transparency in 500 MeV C(pi,pi') Reactions?

The question whether there is a pion transparency in 500 MeV $C(π, π^{'})$ scatterings is studied using a semiclassical, hadronic transport model. The double differential cross sections of this reaction measured at LAMPF can be largely accounted for, if one uses energy-dependent, anisotropic angular distributions which are fitted to pion-nucleon scattering data for the decay of $Δ(1232)$ and $N^*(1440)$ resonances. The remaining discrepancy between the data and the calculation sets a limit on effects of more exotic processes.

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arXiv1996

Excitation functions in central Au+Au collisions from SIS/GSI to AGS/Brookhaven

Using the relativistic transport model (ART), we predict the energy dependence of the stopping power, maximum baryon and energy densities, the population of resonance matter as well as the strength of the transverse and radial flow for central Au+Au reactions at beam momentum from 2 to 12 GeV/c available at Brookhaven's AGS. The maximum baryon and energy densities are further compared to the predictions of relativistic hydrodynamics assuming the formation of shock waves. We also discuss the Fermi-Landau scaling of the pion multiplicity in these reactions.

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arXiv1995

Pion flow and antiflow in relativistic heavy-ion collisions

Within the framework of a relativistic transport model (ART) for heavy-ion collisions at AGS energies, we study the transverse flow of pions with respect to that of nucleons using two complementary approaches. It is found that in central collisions pions develop a weak flow as a result of the flow of baryon resonances from which they are produced. On the other hand, they have a weak antiflow in peripheral collisions due to the shadowing of spectators. Furthermore, it is shown that both pion flow and antiflow are dominated by those with large transverse momenta.

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arXiv1995

Formation of superdense hadronic matter in high energy heavy-ion collisions

We present the detail of a newly developed relativistic transport model (ART 1.0) for high energy heavy-ion collisions. Using this model, we first study the general collision dynamics between heavy ions at the AGS energies. We then show that in central collisions there exists a large volume of sufficiently long-lived superdense hadronic matter whose local baryon and energy densities exceed the critical densities for the hadronic matter to quark-gluon plasma transition. The size and lifetime of this matter are found to depend strongly on the equation of state. We also investigate the degree and time scale of thermalization as well as the radial flow during the expansion of the superdense hadronic matter. The flow velocity profile and the temperature of the hadronic matter at freeze-out are extracted. The transverse momentum and rapidity distributions of protons, pions and kaons calculated with and without the mean field are compared with each other and also with the preliminary data from the E866/E802 collaboration to search for experimental observables that are sensitive to the equation of state. It is found that these inclusive, single particle observables depend weakly on the equation of state. The difference between results obtained with and without the nuclear mean field is only about 20\%. The baryon transverse collective flow in the reaction plane is also analyzed. It is shown that both the flow parameter and the strength of the ``bounce-off'' effect are very sensitive to the equation of state. In particular, a soft equation of state with a compressibility of 200 MeV results in an increase of the flow parameter by a factor of 2.5 compared to the cascade case without the mean field. This large effect makes it possible to distinguish the predictions from different theoretical models and to detect the signatures

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