Yongseok Oh

Nucleon and Delta resonances in K Sigma(1385) photoproduction from nucleons

The reaction mechanisms for K{sigma}(1385) photoproduction from the reaction {gamma}p{yields}K{sup +}{sigma}{sup 0}(1385) in the resonance energy region are investigated in a hadronic model. Both contributions from N and {delta} resonances of masses around 2 GeV as given in the Review of Particle Data Group and by the quark model predictions are included. The Lagrangians for describing the decays of these resonances into K{sigma}(1385) are constructed with the coupling constants determined from the decay amplitudes predicted by a quark model. Comparing the resulting total cross section for the reaction {gamma}p{yields}K{sup +}{sigma}{sup 0}(1385) with the preliminary data from the Thomas Jefferson National Accelerator Facility, we find that the most important contributions are from the two-star-rated resonances {delta}(2000)F{sub 35},{delta}(1940)D{sub 33}, and N(2080)D{sub 13}, as well as the missing resonance N(3/2){sup -}(2095) predicted in the quark model. Predictions on the differential cross section and photon asymmetry in this reaction are also given.

Isospin-dependent pion in-medium effects on the charged-pion ratio in heavy ion collisions

Using results from the chiral perturbation theory for the s-wave interaction and the {Delta}-resonance model for the p-wave interaction of pions with nucleons, we evaluated the spectral functions of pions in asymmetric nuclear matter with unequal proton and neutron densities. We find that in hot dense neutron-rich matter the strength of the spectral function of positively charged pions at low energies is somewhat larger than that of negatively charged pions. In a thermal model, this isospin-dependent effect slightly reduces the ratio of negatively charged to positively charged pions that are produced in heavy ion collisions induced by radioactive beams. The relevance of our results to the determination of the nuclear symmetry energy from the measured ratio of negatively to positively charged pions produced in heavy ion collisions is discussed.

Medium effects in ρ-meson photoproduction

Abstract We compute dilepton invariant mass spectra from the decays of ρ mesons produced by photon reactions off nuclei. Our calculations employ a realistic model for the ρ photoproduction amplitude on the nucleon which provides fair agreement with measured cross sections. Medium effects are implemented via an earlier constructed ρ propagator based on hadronic many-body theory. At incoming photon energies of 1.5–3 GeV as used by the CLAS experiment at JLAB, the average density probed for iron targets is estimated at about half saturation density. At the pertinent 3-momenta the predicted medium effects on the ρ propagator are rather moderate. The resulting dilepton spectra approximately agree with recent CLAS data.

Deuteron production and elliptic flow in relativistic heavy ion collisions

The hadronic transport model ART is extended to include the production and annihilation of deuterons via the reactions BB{r_reversible}dM, where B and M stand for baryons and mesons, respectively, as well as their elastic scattering with mesons and baryons in the hadronic matter. This new hadronic transport model is used to study the transverse momentum spectrum and elliptic flow of deuterons in relativistic heavy ion collisions, with the initial hadron distributions after hadronization of the produced quark-gluon plasma taken from a blast wave model. The results are compared with those measured by the PHENIX and STAR Collaborations for Au+Au collisions at {radical}(s{sub NN})=200 GeV and also with those obtained from the coalescence model based on freeze-out nucleons in the transport model.

Elliptic flow of deuterons in relativistic heavy-ion collisions

Using a dynamical model based on the NN{yields}d{pi},NNN{yields}dN, and NN{pi}{yields}d{pi} reactions and measured proton and pion transverse momentum spectra and elliptic flows, we study the production of deuterons and their elliptic flow in heavy-ion collisions at RHIC. The results are compared with those from the coalescence model. The deviation of deuteron elliptic flow from the constituent nucleon number scaling expected from the coalescence model and the comparison with the experimental data are discussed in connection to the allowed nucleon phase space in these reactions.

J/psi absorption by nucleons in the meson-exchange model

We reinvestigate the

Nuclear modification factor of nonphotonic electrons in heavy-ion collisions, and the heavy-flavor baryon-to-meson ratio

J/ensuremath{psi}

Transport model study of deuteron production in relativistic heavy ion collisions

dissociation processes induced by the reactions with nucleons,

Medium effects in ?-meson photoproduction

J/ensuremath{psi}+Nensuremath{rightarrow}{overline{D}}^{(*)}+{ensuremath{Lambda}}_{c}