arXiv subjects
Publications and source records attributed to K. Tsushima.
The quark-meson coupling (QMC) model is applied to a study of the mass of the $ρ$-meson in helium and carbon nuclei. The average mass of a $ρ$-meson formed in $^{3,4}$He and $^{12}$C is expected to be around 730, 690 and 720 MeV, respectively.
The quark-meson coupling model, based on a mean-field description of non-overlapping nucleon bags bound by the self-consistent exchange of $σ$, $ω$ and $ρ$ mesons, is extended to investigate the change of hadron properties in finite nuclei. Relativistic Hartree equations for spherical nuclei have been derived from a relativistic quark model of the structure of bound nucleons and mesons. Using this unified, self-consistent description of both infinite nuclear matter and finite nuclei, we investigate the properties of some closed-shell nuclei, and study the changes in the hadron masses of the non-strange vector mesons, the hyperons and the nucleon in those nuclei. We find a new, simple scaling relation for the changes of the hadron masses, which can be described in terms of the number of non-strange quarks in the hadron and the value of the scalar mean-field in a nucleus.
Results for the energy dependence of the elementary kaon production cross sections in proton-proton collisions are reported. Calculations are performed within an extended version of the resonance model which was used for the previous studies of elementary kaon production in pion-nucleon and pion-$Δ$ collisions. Although the model treatment is within the {\it empirical} tree level (observed widths for the resonances are used), it is fully relativistic, and includes all relevant baryon resonances up to 2 GeV. One of the purposes of this study is to provide the results for the simulation codes of subthreshold kaon production in heavy ion collisions. This is the first, consistent study of the elementary kaon production reactions including both $πB$ and $B B$ ($B=N, Δ$) collisions on the same footing. Comparisons are made between the calculated results and the existing semi-empirical parametrizations which are widely used for the simulation codes, as well as the experimental data.
We study the $Δ$-excitation in $\overline{p}d$ annihilation at rest. The invariant spectra of the $π^+p$ and $π^-p$ systems selecting the protons with momenta above 400 MeV/c are analyzed. The calculations reproduces reasonably the experimental data.
Parametrizations of total cross sections sufficient for all channels of the $πB \rightarrow Y K$ reactions are completed using a resonance model. As well as discussing the $πN \rightarrow ΛK$ reactions, which were not presented in our previous publications, we present the differential cross section for $πN \rightarrow ΛK$. This report also aims at presenting supplementary discussions to our previous work.
The $Δ$-excitation in $\overline{p}d$ annihilation at rest was studied. The annihilation amplitude from the statistical model and the $πN$ amplitude from the resonance model were adopted in our calculations. We analyze the invariant mass of the $π^+p$ and $π^-p$ systems selecting the protons with momenta above 400 MeV/c and with respect to the different final reaction channels. Our model reproduces reasonably the experimental data.
The isobar model and the resonance model are applied for the first analysis of the subthreshold $K^+$-meson production in proton-carbon collisions, which was perfomed at GSI at an emission angle of 40 degrees and a bombarding energy of 1.2 GeV. In this study, we focus on the role of the secondary processes $πN \to K^+ Y$ in normal nuclear matter density. It turns out that the present approach can reproduce very well both the $π^+$- and $K^+$- meson spectra. It is also demonstrated that the different kinds of descriptions for the $πN \to K^+ Λ$ reactions substantially differentiate the calculated results for the $p A \to K^+ X$ differential cross sections.
The narrow peak recently found in various pionic double charge exchange (DCX) cross sections can be explained by the assumption of a universal resonance at 2065 MeV, called d'. We calculate the mass of a six-quark system with J^P=0^-, T=0 quantum numbers employing a cluster model and a shell model basis to diagonalize the nonrelativistic quark model Hamiltonian.
We study the effect of the density dependence of the scalar and the vector part of the nucleonic self-energy in Relativistic Quantum Molecular Dynamics (RQMD) on observables like the transversal flow and the rapidity distribution. The stability of nuclei in RQMD is greatly improved if the density dependence is included in the self-energies compared to a calculation assuming always saturation density of nuclear matter. Different approaches are studied: The main results are calculated with self-energies extracted from a Dirac-Brückner-Hartree-Fock G-matrix of a one boson exchange model, i.e. the Bonn potential. These results are compared with those obtained by a generalization of static Skyrme force, with calculations in the simple linear Walecka model and results of the Brückner-Hartree-Fock G-matrix of the Reid soft core potential. The transversal flow is very sensitive to these different approaches. A comparison with the data is given.
In a resonance model the reactions pi N -> Y K and pi Delta -> Y K are studied. For the reactions pi N -> Lambda K and pi Delta -> Lambda K, the resonances N(1650)(J^P=1/2^-), N(1710)(1/2^+) and N(1720)(3/2^+) are included as intermediate states. For the reactions pi N -> Sigma K, the resonances N(1710)(1/2^+), N(1720)(3/2^+) and Delta(1920)(3/2^+) are considered, while for the pi Delta -> Sigma K reactions the intermediate resonances are N(1710)(1/2^+) and N(1720)(3/2^+). Besides these resonances in the s-channel, the t-channel K^*(892) exchanges are also taken into account as a smooth background. The relevant coupling constants for the meson-baryon vertices are obtained (except for Delta(1920)) from the experimental decay branching ratios of the relevant resonances. All isospin channels of the pi N -> Y K and pi Delta -> Y K cross sections are calculated. By comparing the calculated results with the available experimental data, we find that the total cross sections of the pi N -> Y K reactions can be explained by the resonance model. The pi Delta -> Y K cross sections, for which no experimental data are available, are predicted theoretically. Parametrizations of the calculated total cross sections for all different isospin channels are given for the use of kaon productions in heavy ion collisions. The differential cross sections are also studied.
The long mean free path of $K^+$ mesons in nuclear matter makes this particle a suitable messenger for the dynamics of nucleus-nucleus reactions at intermediate energies (100 MeV to 3 GeV per nucleon). A prerequisite for this is the knowledge of the elementary production cross sections $πN \rightarrow ΣK$. Here these cross sections are studied for the first time with the explicite inclusion of the relevant baryon resonances up to 2 GeV as intermediate states. The baryon resonances -- $N(1710)\, I(J^P) = \frac{1}{2} (\frac{1}{2}^+),\, N(1720)\, \frac{1}{2} (\frac{3}{2}^+)$ and $Δ(1920)\, \frac{3}{2} (\frac{3}{2}^+)\,$ -- are taken into account coherently in the calculations of the $πN \rightarrow ΣK$ process. (We refer to this model as the `resonance model'.) Also $K^*(892)\frac{1}{2} (1^-)$ vector meson exchange is included. It is shown that the total cross sections for different channels of the $πN \rightarrow Σk$ reactions, i.e. $π^+ p \rightarrow Σ^+ K^+$, $π^- p \rightarrow Σ^- K^+$, $π^+ n \rightarrow Σ^0 K^+$ ($π^- p \rightarrow Σ^- K^+$) and $π^0 p \rightarrow Σ^0 K^+$ differ not only by absolute values but also by their energy dependence. This shape differences are due to the mixture of the isospin $I = 3/2$ $Δ(1920)$ with isospin $I = 1/2$ nucleon resonances. However, this $I = 3/2$ resonance does not give a contribution to the $πN \rightarrow ΛK$ reactions. So the shapes of the total cross sections $πN \rightarrow ΛK$ for different isospin projections are the same. In spite of this, such cross sections averaged over different isospin projections in the same multiplet
The elementary production cross sections $πΔ\rightarrow Y K$ $(Y=Σ,\,\, Λ)$ and $πN \rightarrow Y K$ are needed to describe kaon production in heavy ion collisions. The $πN \rightarrow Y K$ reactions were studied previously by a resonance model. The model can explain the experimental data quite well \cite{tsu}. In this article, the total cross sections $πΔ\rightarrow Y K$ at intermediate energies (from the kaon production threshold to3 GeV of $πΔ$ center-of-mass energy) are calculated for the first time using the same resonance model. The resonances, $N(1710)\,I(J^P) = \frac{1}{2}(\frac{1}{2}^+)$ and $N(1720)\, \frac{1}{2} (\frac{3}{2}^+)$ for the $πΔ\rightarrow ΣK$ reactions, and $N(1650)\, \frac{1}{2} (\frac{1}{2}^-)$, $N(1710)\, \frac{1}{2} (\frac{1}{2}^+)$ and $N(1720)\, \frac{1}{2} (\frac{3}{2}^+)$ for the $πΔ\rightarrow ΛK$ reactions are taken into account coherently as the intermediate states in the calculations. Also t-channel $K^*(892) \frac{1}{2}(1^-)$ vector meson exchange is included. The results show that $K^*(892)$ exchange is neglegible for the $πΔ\rightarrow ΣK$ reactions, whereas this meson does not contribute to the $πΔ\rightarrow ΛK$ reactions. Furthemore, the $πΔ\rightarrow Y K$ contributions to kaon production in heavy ion collisions are not only non-neglegible but also very different from the $πN \rightarrow Y K$ reactions. An argument valid for $πN \rightarrow Y K$ cannot be extended to $πΔ\rightarrow Y K$ reactions. Therefore, cross sections for $πΔ\rightarrow Y K$ including correctly the different isospins must be
The axial exchange current operator that arises from the coupling of the axial field to the pion and effective scalar field in nuclei is constructed. The spatial dependence of this exchange current operator may be determined directly from the nucleon-nucleon interaction. This "$πσ$"-axial exchange current contributes about 5\% to the quenching of the nucleon axial current coupling constant $g_A^{GT}$ in heavy nuclei.
We show that the predicted hyperon masses in the topological soliton model are very sensitive to the value of the gluon condensate parameter that appears when the scale invariance and trace anomaly of QCD are taken into account by introduction of a dilaton field. This contrasts with the insensitivity of the soliton properties to the dilaton coupling. In order that the predicted strange and charmed hyperon spectra agree with the empirical ones the gluon condensate parameter has to be about (400 MeV)$^4$, which agrees with the result obtained from QCD sum rules. This implies that the bag formed by the scalar field must be very shallow.