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Yongseok Oh

Publications and source records attributed to Yongseok Oh.

At least 73 records · Page 4Linked to original sources
arXiv2011

Role of high-spin hyperon resonances in the reaction of $γp \to K^+ K^+ Ξ^-$

The recent data taken by the CLAS Collaboration at the Thomas Jefferson National Accelerator Facility for the reaction of $γp \to K^+ K^+ Ξ^-$ are reanalyzed within a relativistic meson-exchange model of hadronic interactions. The present model is an extension of the one developed in an earlier work by Nakayama, Oh, and Haberzettl [Phys. Rev. C 74, 035205 (2006)]. In particular, the role of the spin-5/2 and -7/2 hyperon resonances, which were not included in the previous model, is investigated in the present study. It is shown that the contribution of the $Σ(2030)$ hyperon having spin-7/2 and positive parity has a key role to bring the model predictions into a fair agreement with the measured data for the $K^+Ξ^-$ invariant mass distribution.

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arXiv2010

Photoproduction of K Sigma(1385) from the nucleon

The reactions of $K Σ(1385)$ photoproduction, i.e., $γp \to K^+ Σ^0(1385)$ and $γn \to K^+ Σ^-(1385)$, are investigated in the resonance energy region for studying the role of the nucleon and $Δ$ resonances of masses around 2 GeV. The Lagrangians for describing the decays of these resonances into the $K Σ(1385)$ channel are constructed and the decay amplitudes are obtained, which allows us to determine the coupling constants using the predictions of quark models or the data listed by the Particle Data Group. The resulting cross sections are compared to the data from the Thomas Jefferson National Accelerator Facility and the SPring-8, which indicates nontrivial contributions from the two-star-rated resonances in the Particle Data Group as well as from some missing resonances predicted by a quark model.

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arXiv2010

Medium Modifications of the Rho Meson in Nuclear Photoproduction

We extend our recent study of dilepton invariant-mass spectra from the decays of rho mesons produced by photon reactions off nuclei. We specifically focus on experimental spectra as recently measured by the CLAS Collaboration at the Thomas Jefferson National Accelerator Facility using carbon and iron nuclei. Building on our earlier work we broaden our description to a larger set of observables in order to identify sensitivities to the medium effects predicted by microscopic calculations of the rho spectral function. We compute mass spectra for several target nuclei and study the spectral shape as a function of the 3-momentum of the outgoing lepton pair. We also compute the so-called nuclear transparency ratio which provides an alternative means (and thus consistency check) of estimating the inelastic rho width in the cold nuclear medium.

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arXiv2010

Isospin-dependent pion in-medium effects on 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 have 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 pion at low energies is somewhat larger than that of negatively charged pion. 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. Relevance of our results to the determination of the nuclear symmetry energy from measured ratio of negatively to positively charged pions produced in heavy ion collisions is discussed.

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arXiv2010

Medium effects on charged pion ratio in heavy ion collisions

We have recently studied in the delta-resonance--nucleon-hole model the dependence of the pion spectral function in hot dense asymmetric nuclear matter on the charge of the pion due to the pion p-wave interaction in nuclear medium. In a thermal model, this isospin-dependent effect enhances the ratio of negatively charged to positively charged pions in neutron-rich nuclear matter, and the effect is comparable to that due to the uncertainties in the theoretically predicted stiffness of nuclear symmetry energy at high densities. This effect is, however, reversed if we also take into account the s-wave interaction of the pion in nuclear medium as given by chiral perturbation theory, resulting instead in a slightly reduced ratio of negatively charged to positively charged pions. Relevance of our results to the determination of the nuclear symmetry energy from the ratio of negatively to positively charged pions produced in heavy ion collisions is discussed.

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arXiv2009

Deuteron production and elliptic flow in relativistic heavy ion collisions

The hadronic transport model \textsc{art} is extended to include the production and annihilation of deuterons via the reactions $BB \leftrightarrow dM$, 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 then 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 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 $\sqrt{s_{NN}^{}} = 200$ GeV, and also with those obtained from the coalescence model based on freeze-out nucleons in the transport model.

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arXiv2009

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

The nuclear modification factor $R_{AA}$ of non-photonic electrons in ${Au} + {Au}$ collisions at $\sqrt{s_{NN}^{}} = 200$ GeV is studied by considering the decays of heavy-flavor hadrons produced in a quark coalescence model. Although an enhanced $Λ_c/D^0$ ratio is predicted by the coalescence model, it is peaked at small transverse momenta ($\sim 2$ GeV) due to the large difference between heavy and light quark masses. As a result, the enhanced $Λ_c/D^0$ ratio, which is expected to suppress the electron $R_{AA}$ as the branching ratio of $Λ_c$ decay into electrons is smaller than that of $D^0$, does not lead to additional suppression of the electron $R_{AA}$ at large transverse momenta ($\ge 5$ GeV), where the suppression is mainly due to heavy quark energy loss in produced quark-gluon plasma. Also, the enhanced $Λ_b/\bar{B}^0$ ratio predicted by the coalescence model has even smaller effect on the non-photonic electron $R_{AA}$ as bottom baryons and mesons have similar branching ratios for semi-leptonic decays into electrons.

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arXiv2009

Medium Effects in rho-Meson Photoproduction

We compute dilepton invariant mass spectra from the decays of rho mesons produced by photon reactions off nuclei. Our calculations employ a realistic model for the rho photoproduction amplitude on the nucleon which provides fair agreement with measured cross sections. Medium effects are implemented via an earlier constructed rho 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 rho-meson 3-momenta the predicted medium effects on the rho propagator are rather moderate. The resulting dilepton spectra approximately agree with recent CLAS data.

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arXiv2009

Heavy baryon/meson ratios in relativistic heavy ion collisions

Heavy baryon/meson ratios $Λ_c/D^0$ and $Λ_b/\bar{B}^0$ in relativistic heavy ion collisions are studied in the quark coalescence model. For heavy baryons, we include production from coalescence of heavy quarks with free light quarks as well as with bounded light diquarks that might exist in the strongly coupled quark-gluon plasma produced in these collisions. Including the contribution from decays of heavy hadron resonances and also that due to fragmentation of heavy quarks that are left in the system after coalescence, the resulting $Λ_c/D^0$ and $Λ_b/\bar{B}^0$ ratios in midrapidity ($|y|\le 0.5$) from central Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV are about a factor of five and ten, respectively, larger than those given by the thermal model, and about a factor of ten and twelve, respectively, larger than corresponding ratios in the PYTHIA model for $pp$ collisions. These ratios are reduced by a factor of about 1.6 if there are no diquarks in the quark-gluon plasma. The transverse momentum dependence of the heavy baryon/meson ratios is found to be sensitive to the heavy quark mass, with the $Λ_b/\bar{B}^0$ ratio being much flatter than the $Λ_c/D^0$ ratio. The latter peaks at the transverse momentum $p_T^{} \simeq 0.8$ GeV but the peak shifts to $p_T^{} \simeq 2$ GeV in the absence of diquarks.

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arXiv2008

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

The reaction mechanisms for $KΣ(1385)$ photoproduction from the reaction $γp \to K^+Σ^{0}(1385)$ in the resonance energy region are investigated in a hadronic model. Both contributions from $N$ and $Δ$ 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 $KΣ(1385)$ 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 $γp \to K^+Σ^{0}(1385)$ 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 $Δ(2000) F_{35}$, $Δ(1940) D_{33}$, and $N(2080) D_{13}$, as well as the missing resonance $N\frac32^-(2095)$ predicted in the quark model. Predictions on the differential cross section and photon asymmetry in this reaction are also given.

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arXiv2007

Elliptic flow of deuterons in relativistic heavy-ion collisions

Using a dynamical model based on the $NN \to dπ$, $NNN \to dN$, and $NNπ\to dπ$ 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.

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arXiv2007

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

We reinvestigate the $J/ψ$ dissociation processes induced by the reactions with nucleons, $J/ψ+ N \to \bar{D}^{(*)} + Λ_c$, in the meson-exchange model. Main constraints used in this work are vector-meson dominance and charm vector-current conservation. We show that the cross section for $J/ψ+ N \to \bar{D} + Λ_c$ can be larger than that for $J/ψ+ N \to \bar{D}^{*} + Λ_c$ when these constraints are imposed. The dependence of the cross sections on the coupling constants is analyzed in detail, and the comparison with the recent quark-interchange model predictions is also made.

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arXiv2007

On the sign of the pi-rho-omega coupling constant

It is shown that the relative sign between the $NNω$ and $πρω$ coupling constants can be determined most sensitively from $ω$ production processes in $NN$ collisions. Recent data on these reactions clearly favor the sign of the $πρω$ coupling constant which is opposite to that inferred from studies of the photoproduction reaction in combination with the vector meson dominance assumption and used by many authors. Implication of this finding in the description of other reactions is discussed.

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arXiv2007

Xi and Omega baryons in the Skyrme model

The mass spectrum and magnetic moments of Ξand Ωbaryon resonances are investigated in the bound state approach of the Skyrme model. The empirical hyperon spectrum shows that several hyperon resonances share a pattern of (approximately) equal mass spacings between the states of same spin but of opposite parity. It is found that this pattern can be explained mostly by the energy difference between the P-wave and S-wave kaons bound to the soliton. Although one cannot exclude the possibility that these states can be described as pion-hyperon resonances, the present approach predicts that Ξ(1620) and Ξ(1690) have J^P = 12^-, while Ξ(1950) has J^P = 12^+. The differences with the quark model predictions for the Ξand Ωbaryon spectrum are pointed out. Several relations for the masses and magnetic moments of those resonances are also obtained.

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arXiv2006

Photoproduction of Xi off nucleons

The photoproduction reaction $γN \to K K Ξ$ is investigated based on a relativistic meson-exchange model of hadronic interactions. The production amplitude is calculated in the tree-level approximation from relevant effective Lagrangians, whose (coupling constant) parameters are mostly fixed from the empirical data and/or quark models together with SU(3) symmetry considerations. Gauge invariance of the resulting amplitude is maintained by introducing the contact currents by extending the gauge-invariant approach of Haberzettl for one-meson photoproduction to two-meson photoproduction. The role of the intermediate low-lying hyperons and of the intermediate higher-mass hyperon resonances are analyzed in detail. In particular, the basic features of the production of $Ξ^-(1318)$ in $γp \to K^+ K^+ Ξ^-$ and their possible manifestations in the forthcoming experimental data are discussed.

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arXiv2006

Scalar kappa meson in K* photoproduction

We propose that the scalar $κ(800)$ meson may play an important role in $K^*$ photoproduction. In the reactions of $γp \to K^{*+} Λ$ and $γp \to K^{*0} Σ^+$, we consider the production mechanisms including $t$-channel $K^*$, $K$, $κ$ exchanges, s-channel $N$, $Δ$ diagrams, and $u$-channel $Λ$, $Σ$, $Σ^*$ diagrams within the tree level approximation, and find that the $κ$-meson exchange may contribute significantly to $K^*Σ$ photoproduction, while it is rather supplementary in $K^*Λ$ photoproduction. We demonstrate how the observables of $K^*$ photoproduction can be used to constrain the $κ$ meson properties. In particular, the parity asymmetry can separate the $κ$ meson contribution in $K^*$ photoproduction.

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arXiv2006

K* photoproduction off the nucleon: gamma N --> K* Lambda

We study the photoproduction of $K^*(892)$ vector meson from both the charged and neutral reactions, $γp \to K^{*+} Λ$ and $γn \to K^{*0} Λ$. The production mechanisms that we consider include $t$-channel $K^*$, $K$, $κ$ exchanges, s-channel nucleon diagram, and $u$-channel $Λ$, $Σ$, $Σ^*$ diagrams. These could constitute important backgrounds for future investigation of ``missing'' resonances that can be searched for especially in these reactions. The $t$-channel $K$ meson exchange is found to dominate both reactions. The total and differential cross sections are presented together with some spin asymmetries.

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