Browsing by Author "Ko, Che Ming"
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Item Anomalous transport model study of chiral magnetic effects in heavy ion collisions(Physical Review C - Nuclear Physics, 2016) Sun, Yifeng; Ko, Che Ming; Li, FengItem Antiflow of kaons in relativistic heavy ion collisions(American Physical Society, 2000) Pal, S.; Ko, Che Ming; Lin, ZW; Zhang, B.We compare relativistic transport model calculations to recent data on the sideward flow of neutral strange K-s(0) mesons for Au+Au collisions at 6A GeV. A soft nuclear equation of state is found to describe very well the positive proton flow data measured in the same experiment. In the absence of the kaon potential, the K-0 flow pattern is similar to that of protons. The kaon flow becomes negative if a repulsive kaon potential determined from the impulse approximation is introduced. However, this potential underestimates the data which exhibit larger antiflow. An excellent agreement with the data is obtained when a relativistic scalar-vector kaon potential, that has stronger density dependence, is used. We further find that the transverse momentum dependence of directed and elliptic flow is quite sensitive to the kaon potential in dense matter.Item Antilambda Enhancement in Ultrarelativistic Heavy-Ion Collisions(American Physical Society, 1992) Ko, Che Ming; Asakawa, M.; Levai, P.In the Walecka model, the antilambda mass in dense nuclear matter is smaller than its value in free space. This reduces the threshold for antilambda production in dense matter that forms in the compression stage of ultrarelativistic heavy ion collisions. Because of the large number of mesons produced in the collision, the process KM --> LAMBDA-BAR N, where M denotes either a pion or a rho meson, is shown to be important and provides thus a plausible explanation for the observed enhancement of antilambda yield in recent experiments carried out at CERN SPS with nuclear beams.Item Asymptotic scattering wave function for three charged particles and astrophysical capture processes(Texas A&M University, 2006-08-16) Pirlepesov, Fakhriddin; Tribble, Robert E.; Gagliardi, Carl A.; Ko, Che Ming; Yennello, Sherry J.The asymptotic behavior of the wave functions of three charged particles has been investigated. There are two different types of three-body scattering wave functions. The first type of scattering wave function evolves from the incident three-body wave of three charged particles in the continuum. The second type of scattering wave function evolves from the initial two-body incident wave. In this work the asymptotic three-body incident wave has been derived in the asymptotic regions where two particles are close to each other and far away from the third particle. This wave function satisfies the Schrodinger equation up to terms O(1/3pa), where pa is the distance between the center of mass of two particles and the third particle. The derived asymptotic three-body incident wave transforms smoothly into RedmondÂ’s asymptotic incident wave in the asymptotic region where all three particles are well separated. For the scattering wave function of the second type the asymptotic threebody scattered wave has been derived in all the asymptotic regions. In the asymptotic region where all three particles well separated, the derived asymptotic scattered wave coincides with the Peterkop asymptotic wave. In the asymptotic regions where two particles are close to each other and far away from the third one, this is a new expression which is free of the logarithmically diverging phase factors that appeared in the Peterkop approach. The derived asymptotic scattered wave resolves a long-standing phase-amplitude ambiguity. Based on these results the expressions for the exact prior and post breakup amplitudes have been obtained. The post breakup amplitude for charged particles has not been known and has been derived for the first time directly from the prior form. It turns out that the post form of the breakup amplitude is given by a surface integral in the six dimensional hyperspace, rather than a volume integral, with the transition operator expressed in terms of the interaction potentials. We also show how to derive a generalized distorted-wave-Born approximation amplitude (DWBA) from the exact prior form of the breakup amplitude. It is impossible to derive the DWBA amplitude from the post form. The three-body Coulomb incident wave is used to calculate the reaction rates of 7Be(ep, e)8B and 7Be(pp, p)8B nonradiative triple collisions in stellar environments.Item Bottomonia suppression in relativistic heavy-ion collisions(Physical Review C - Nuclear Physics, 2012) Song, Taesoo; Han, Kyong Chol; Ko, Che MingItem Calculation of Kr and Xe Induced Deeply Inelastic Heavy-Ion Collisions with Help of a Transport-Equation(American Physical Society, 1978) Agassi, D.; Ko, Che Ming; Weidenmuller, H. A.Item Charged particle rapidity distributions at relativistic energies(American Physical Society, 2001) Lin, ZW; Pal, S.; Ko, Che Ming; Li, Ba; Zhang, B.Using a multiphase transport model (AMPT), which includes both initial partonic and final hadronic interactions, we study the rapidity distributions of charged particles such as protons, antiprotons, pions, and kaons in heavy ion collisions at RHIC. The theoretical results for the total charged particle multiplicity at midrapidity are consistent with those measured by the PHOBOS Collaboration in central Au+Au collisions at roots = 56 and 130A GeV. We find that these hadronic observables are much more sensitive to the hadronic interactions than to the partonic interactions.Item Charmed exotics in heavy ion collisions(The European Physical Journal C - Particles and Fields, 2008) Lee, Su Houng; Yasui, Shigehiro; Liu, Wei; Ko, Che MingItem Charmonium production from nonequilibrium charm and anticharm quarks in quark-gluon plasma(Physical Review C - Nuclear Physics, 2012) Song, Taesoo; Han, Kyong Chol; Ko, Che MingItem Charmonium production in relativistic heavy-ion collisions(Physical Review C - Nuclear Physics, 2011) Song, Taesoo; Han, Kyong Chol; Ko, Che MingItem Chiral Magnetic and Vortical Effects in Relativistic Heavy Ion Collisions(2017-12-04) Sun, Yifeng; Ko, Che Ming; Folden III, Charles M.; Fries, Rainer; Rapp, Ralf; Gagliardi, Carl A.In the present dissertation, the derivation of the chiral magnetic effect (CME) and chiral separation effect (CSE) from the Hamiltonian of Dirac fermions in a magnetic field is given. It is shown that the CSE is related to the spin polarization vector of massless fermions and becomes less important when fermions are massive. The chiral kinetic equations for massless fermions in a magnetic field are also derived from the Lagrangian of a massless fermion either using the semiclassical approximation or by solving the Dirac equation. The chiral vortical effect (CVE) and chiral vortical separation effect (CVSE) are similarly derived as for the case of the CME and CSE. The interplay between the vector and axial vector charge densities can generate two kinds of gapless collective modes, called the chiral magnetic wave (CMW) and the chiral vortical wave (CVW), and both can be derived in the hydrodynamic and kinetic approaches. Effects of the CMW and CVW in relativistic heavy ion collisions are then studied by solving the chiral kinetic equations numerically using the testparticle method. It is found that, the CMW generated by the magnetic field in a quark matter with its initial conditions modeled by the Bjorken boost-invariant model can lead to different elliptic flows for particles of positive and negative charges if the chirality changing scattering (CCS) between massless quarks and antiquarks is included. Neglecting the Lorentz force acting on quarks and antiquarks as in other studies, it is found that the obtained elliptic flow splitting depends linearly on the charge asymmetry of the quark matter, similar to that measured in experiments at RHIC. The magnitude of the splitting is, however, less than the experimental results even if the magnetic field is taken to have a long lifetime. The presence of a vorticity field in the quark matter is found to only lead to an axial dipole moment in the transverse plane but not an elliptic flow splitting between particles of positive and negative charges. Including effects from both the magnetic field and the vorticity field can, on the other hand, leads to the splitting between the elliptic flows of positivelyand negatively charged particles even for quark matter of zero charge asymmetry. However, the inclusion of the Lorentz force changes the sign of the slope of the charge asymmetry dependence of the elliptic flow splitting, leading to a result opposite to that from the experiments and thus making it unlikely that the observed elliptic flow splitting between charged particles is due to the CMW. Including in quark scattering the correction to the phase-space measure due to the vorticity field, the chiral kinetic equations are also used to study the spin polarization of light quarks in a rotating quark matter with its initial conditions taken from a multiphase transport (AMPT) model. Converting the spin-polarized light quarks to hadrons using the quark coalescence model leads to the spin polarizations of Ʌ and Ʌ ¯ (bar should be over Ʌ) hyperons that are comparable with experimental results both in magnitude and trend as a function of collision energy.Item Collision energy dependence of elliptic flow splitting between particles and their antiparticles from an extended multiphase transport model(Physical Review C - Nuclear Physics, 2016) Xu, Jun; Ko, Che MingItem Contribution of Pi-N-]Lambda-K to Subthreshold Kaon Production in Heavy-Ion Collisions(American Physical Society, 1990) Xiong, L.; Ko, Che Ming; Wu, J. Q.Item Contributions of hyperon-hyperon scattering to subthreshold cascade production in heavy ion collisions(Physical Review C - Nuclear Physics, 2012) Li, Feng; Chen, Lie-Wen; Ko, Che Ming; Lee, Su HoungItem Cross section for charmonium absorption by nucleons(American Physical Society, 2002) Liu, W.; Ko, Che Ming; Lin, ZW.The cross section for J/psi absorption by nucleons is studied using a gauged SU(4) hadronic Lagrangian but with empirical particle masses, which has been used previously to study the cross sections for J/psi absorption by pion and rho meson. Including both two-body and three-body final states, we find that with a cutoff parameter of 1 GeV at interaction vertices involving charm hadrons, the J/psi-N absorption cross section is at most 5 mb and is consistent with that extracted from J/psi production from both photonuclear and proton-nucleus reactions.Item D-sJ(2317) meson production in ultrarelativistic heavy ion collisions RID A-2398-2009(American Physical Society, 2007) Chen, L. W.; Ko, Che Ming; Liu, W.; Nielsen, M.Production of D-sJ(2317) mesons in relativistic heavy ion collisions at the BNL Relativistic Heavy Ion Collider is studied. Using the quark coalescence model, we first determine the initial number of D-sJ(2317) mesons produced during hadronization of created quark-gluon plasma. The predicted D-sJ(2317) abundance depends sensitively on the quark structure of the D-sJ(2317) meson. An order-of-magnitude larger yield is obtained for a conventional two-quark than for an exotic four-quark D-sJ(2317) meson. To include the hadronic effect on the D-sJ(2317) meson yield requires the absorption cross sections of the D-sJ(2317) meson by pions, rho mesons, anti-kaons, and vector anti-kaons, which we have evaluated in a phenomenological model. Taking into consideration the absorption and production of D-sJ(2317) mesons during the hadronic stage of heavy ion collisions via a kinetic model, we find that the final yield of D-sJ(2317) mesons remains sensitive to its initial number produced from the quark-gluon plasma, providing thus the possibility of studying the quark structure of the D-sJ(2317) meson and its production mechanism in relativistic heavy ion collisions.Item Density slope of the nuclear symmetry energy from the neutron skin thickness of heavy nuclei(American Physical Society, 2010) Chen, Lie-Wen; Ko, Che Ming; Li, Bao-An; Xu, Jun.Expressing explicitly the parameters of the standard Skyrme interaction in terms of the macroscopic properties of asymmetric nuclear matter, we show in the Skyrme-Hartree-Fock approach that unambiguous correlations exist between observables of finite nuclei and nuclear matter properties. We find that existing data on neutron skin thickness Delta r(np) of Sn isotopes give an important constraint on the symmetry energy E(sym)(rho(0)) and its density slope L at saturation density rho(0). Combining these constraints with those from recent analyses of isospin diffusion and the double neutron/proton ratio in heavy-ion collisions at intermediate energies leads to a more stringent limit on L approximately independent of E(sym)(rho(0)). The implication of these new constraints on the Delta r(np) of (208)Pb as well as the core-crust transition density and pressure in neutron stars is discussed.Item Determination of the Stiffness of the Nuclear Symmetry Energy from Isospin Diffusion(Physical Review Letters, 2005) Chen, Lie-Wen; Ko, Che Ming; Li, Bao-AnItem Dielectron Production in Proton-Nucleus Reactions(American Physical Society, 1990) Xiong, L.; Wu, J. Q.; Wu, Z. G.; Ko, Che Ming; Shi, J. H.Item Dilepton as a Possible Signature for the Baryon-Rich Quark-Gluon Plasma(American Physical Society, 1990) Xia, L. H.; Ko, Che Ming; Li, C. T.