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K. Tsushima

Publications and source records attributed to K. Tsushima.

At least 145 records · Page 8Linked to original sources
arXiv2001

Charmonium absorption by nucleons

$J/Ψ$ dissociation in collisions with nucleons is studied within a boson exchange model and the energy dependence of the dissociation cross section is calculated from the threshold for $Λ_c{\bar D}$ production to high energies. We illustrate the agreement of our results with calculations based on short distance QCD and Regge theory. The compatibility between our calculations and the data on $J/Ψ$ photoproduction on a nucleon is discussed. We evaluate the elastic $J/Ψ{+}N$ cross section using a forward dispersion relation and demonstrate the overall agreement with the predictions from QCD sum rules. Our results are compatible with the phenomenological dissociation cross section evaluated from the experimental data on $J/Ψ$ production from $γ{+}A$, $p{+}A$ and $A{+}A$ collisions.

nucl-th↗
arXiv2000

Kaon properties and cross sections in nuclear medium

Results for the $π+ N \to Λ, Σ+ K$ reactions in nuclear matter of Ref. nucl-th/0004011 are presented. To evaluate the in-medium modification of the reaction amplitude as a function of the baryonic density we introduce relativistic, mean-field potentials for the initial, final and intermediate mesonic and baryonic states in the resonance model. These vector and scalar potentials were calculated using the quark meson coupling model. Contrary to earlier work which has not allowed for the change of the cross section in medium, we find that the data for kaon production at SIS energies are consistent with a repulsive $K^+$-nucleus potential.

nucl-th↗
arXiv2000

In-medium kaon and antikaon properties in the quark-meson coupling model

The properties of the kaon, $K$, and antikaon, $\kbar$, in nuclear medium are studied in the quark-meson coupling (QMC) model. Employing a constituent quark-antiquark (MIT bag model) picture, their excitation energies in a nuclear medium at zero momentum are calculated within mean field approximation. The scalar, and the vector mesons are assumed to couple directly to the nonstrange quarks and antiquarks in the $K$ and $\kbar$ mesons. It is demonstrated that the $ρ$ meson induces different mean field potentials for each member of the isodoublets, $K$ and $\kbar$, when they are embedded in asymmetric nuclear matter. Furthermore, it is also shown that this $ρ$ meson potential is repulsive for the $K^-$ meson in matter with a neutron excess, and renders $K^-$ condensation less likely to occur.

nucl-th↗
arXiv2000

Strangeness production from $πN$ collisions in nuclear matter

Kaon production in pion-nucleon collisions in nuclear matter is studied in the resonance model. To evaluate the in-medium modification of the reaction amplitude as a function of the baryonic density we introduce relativistic, mean-field potentials for the initial, final and intermediate mesonic and baryonic states. These vector and scalar potentials were calculated using the quark-meson coupling (QMC) model. The in-medium kaon production cross sections in pion-nucleon interactions for reaction channels with $Λ$ and $Σ$ hyperons in the final state were calculated at the baryonic densities appropriate to relativistic heavy ion collisions. Contrary to earlier work which has not allowed for the change of the cross section in medium, we find that the data for kaon production are consistent with a repulsive $K^+$-nucleus potential.

nucl-th↗
arXiv2000

Deep inelastic scattering on asymmetric nuclei

We study deep inelastic scattering on isospin asymmetric nuclei. In particular, the difference of the nuclear structure functions and the Gottfried sum rule for the lightest mirror nuclei, 3He and 3H, are investigated. It is found that such systems can provide significant information on charge symmetry breaking and flavor asymmetry in the nuclear medium. Furthermore, we propose a new method to extract the neutron structure function from radioactive isotopes far from the line of stability. We also discuss the flavor asymmetry in the Drell-Yan process with isospin asymmetric nuclei.

nucl-th↗
arXiv2000

Novel features of $J/Ψ$ dissociation in matter

We make a detailed study of the effect that the recently predicted modification of the in-medium masses of charmed mesons would have on $J/Ψ$ dissociation on pion and $ρ$-meson comovers in relativistic heavy ion collisions. We find a substantial dependence of the $J/Ψ$ absorption rates on the density and temperature of the nuclear matter. This suggests that a quantitative analysis of $J/Ψ$ dissociation in nucleus nucleus collisions should include the effects of the modification of meson masses in dense matter.

nucl-th↗
arXiv2000

On the $Λ$ to $Σ^0$ ratio from proton-proton collisions

We compare the recent COSY data on the total $pp{\to}pΛ{K^+}$ and $pp{\to}pΣ^0{K^+}$ cross sections with the predictions from two boson exchange models that either are based solely on $π$ and $K$ exchange or include $π$, $η$ and $ρ$ exchange as well as the virtual excitation of intermediate baryon resonances. Both models are found to reproduce the data after the inclusion of final state hyperon-nucleon interactions. Thus, within the experimental uncertainties, both models also roughly reproduce the strong dependence of the $Λ$ to $Σ^0$ ratio as a function of the excess energy near threshold, as well as at higher energies.

nucl-th↗
arXiv1999

Baryon Masses from Lattice QCD: Beyond the Perturbative Chiral Regime

Consideration of the analytic properties of pion-induced baryon self-energies leads to new functional forms for the extrapolation of light baryon masses. These functional forms reproduce the leading non-analytic behavior of chiral perturbation theory, the correct non-analytic behavior at the $N π$ threshold and the appropriate heavy-quark limit. They involve only three unknown parameters, which may be obtained by fitting to lattice data. Recent dynamical fermion results from CP-PACS and UKQCD are extrapolated using these new functional forms. We also use these functions to probe the limit of applicability of chiral perturbation theory to the extrapolation of lattice QCD results.

hep-lat↗
arXiv1999

On Studying Charm in Nuclei through Antiproton Annihilation

We examine the production of open charm in antiproton annihilation on finite nuclei. The enhancement of the subthreshold production cross section, even in a nucleus as light as carbon, should provide a clean signature of the reduction in the masses of these mesons in-medium. We also show that a careful analysis of the $D^+$ and $D^-$ spectra can yield important information on the cross section for $D^{\pm}N$ scattering.

nucl-th↗
arXiv1999

On the search for a narrow penta-quark Z$^+$ baryon in NN interactions

The possibility for an observation of a narrow penta-quark $Z^+$ baryon in $NN$ reactions is discussed. It is shown that the $pp{\to}nΣ^+K^+$ reaction at excess energies around 100 MeV above threshold provides optimal conditions for $Z^+$ baryon detection by an analysis of the $nK^+$ invariant mass spectrum, if the $Z^+$ mass is located around 1.5 GeV involving a rather narrow width.

nucl-th↗
arXiv1999

Charge symmetry breaking in mirror nuclei from quarks

The binding energy differences of the valence proton and neutron of the mirror nuclei, $^{15}$O -- $^{15}$N, $^{17}$F -- $^{17}$O, $^{39}$Ca -- $^{39}$K and $^{41}$Sc -- $^{41}$Ca, are calculated using the quark-meson coupling (QMC) model. The calculation involves nuclear structure and shell effects explicitly. It is shown that binding energy differences of a few hundred keV arise from the strong interaction, even after subtracting all electromagnetic corrections. The origin of these differences may be ascribed to the charge symmetry breaking effects set in the strong interaction through the u and d current quark mass difference.

nucl-th↗
arXiv1999

Spectral change of sigma and omega mesons in a dense nuclear medium

The spectra of the scalar ($σ$) and vector ($ω$) mesons in nuclear matter are studied in detail using the quark-meson coupling (QMC) model. It is shown that above normal nuclear matter density the effects of $σ$-$ω$ mixing and the decay of the $σ$ into $2π$ change the spectra of $σ$ and $ω$ mesons considerably. As in Quantum Hadrodynamics we find a remarkable spectral change in the $σ$ meson and the longitudinal mode of the $ω$ meson, namely a two-peak structure.

nucl-th↗
arXiv1999

Effect of nucleon structure variation on the longitudinal response function

Using the quark-meson coupling (QMC) model, we study the longitudinal response function for quasielastic electron scattering from nuclear matter. In QMC the coupling constant between the scalar ($σ$) meson and the nucleon is expected to decrease with increasing nuclear density, because of the self-consistent modification of the structure of the nucleon. The reduction of the coupling constant then leads to a smaller contribution from relativistic RPA than in the Walecka model. However, since the electromagnetic form factors of the in-medium nucleon are modified at the same time, the longitudinal response function and the Coulomb sum are reduced by a total of about 20% in comparison with the Hartree contribution. We find that the relativistic RPA and the nucleon structure variation both contribute about fifty-fifty to the reduction of the longitudinal response.

nucl-th↗
arXiv1999

Resonance model study of kaon production in baryon baryon reactions for heavy ion collisions

The energy dependence of the total kaon production cross sections in baryon baryon ($N$ and $Δ$) collisions are studied in the resonance model, which is a relativistic, tree-level treatment. This study is the first attempt to complete a systematic, consistent investigation of the elementary kaon production reactions for both the pion baryon and baryon baryon reactions. Our model suggests that the magnitudes of the isospin-averaged total cross sections for the $N N \to N Y K$ and $ΔN \to N Y K$ ($Y = Λ$ or $Σ$) reactions are almost equal at energies up to about 200 MeV above threshold. However, the magnitudes for the $ΔN$ reactions become about 6 times larger than those for the $N N$ reactions at energies about 1 GeV above threshold. Furthermore, the magnitudes of the isospin-averaged total cross sections for the $N N \to ΔY K$ reactions turn out to be comparable to those for the $N N \to N Y K$ reactions at $N N$ invariant collision energies about 3.1 GeV, and about 5 to 10 times larger at $N N$ invariant collision energies about 3.5 GeV. The microscopic cross sections are parametrized in all isospin channels necessary for the transport model studies of kaon production in heavy ion collisions. These cross sections are then applied in the relativistic transport model to study the sensitivity to the underlying elementary kaon production cross sections.

nucl-th↗
arXiv1999

Fock terms in the quark-meson coupling model

The mean field description of nuclear matter in the quark-meson coupling model is improved by the inclusion of exchange contributions (Fock terms). The inclusion of Fock terms allows us to explore the momentum dependence of meson-nucleon vertices and the role of pionic degrees of freedom in matter. It is found that the Fock terms maintain the previous predictions of the model for the in-medium properties of the nucleon and for the nuclear incompressibility. The Fock terms significantly increase the absolute values of the single-particle, four-component scalar and vector potentials, a feature that is relevant for the spin-orbit splitting in finite nuclei.

nucl-th↗
arXiv1999

Charmed Mesic Nuclei: Bound D and $\bar{D}$ states with ^{208}Pb

We show that the D^- meson will form narrow bound states with ^{208}Pb. Mean field potentials for the D^0, D^0-bar and D^- in ^{208}Pb are calculated self-consistently using the quark-meson coupling (QMC) model in local density approximation. The meson-^{208}Pb bound state energies are then calculated by solving the Klein-Gordon equation with these potentials. The experimental confirmation and comparison with the D^0-bar and D^0 will provide distinctive information on the nature of the interaction between the charmed meson and matter.

nucl-th↗
arXiv1999

Study of Omega, Eta, Eta-prime and D-minus mesic nuclei

Using the quark-meson coupling (QMC) model, we investigate whether $ω, η, η'$ and $D^-$ mesons form meson-nucleus bound states. Our results suggest that one should expect to find $η$- and $ω$-nucleus bound states in all the nuclei considered. Furthermore, it is shown that the $D^-$ meson will form quite narrow bound states with $^{208}$Pb.

nucl-th↗