arXiv subjects

S. W. Huang

Publications and source records attributed to S. W. Huang.

22 records · Page 2Linked to original sources

arXiv1995

Consequences of a covariant Description of Heavy Ion Reactions at intermediate Energies

Heavy ion collisions at intermediate energies are studied by using a new RQMD code, which is a covariant generalization of the QMD approach. We show that this new implementation is able to produce the same results in the nonrelativistic limit (i.e. 50MeV/nucl.) as the non-covariant QMD. Such a comparison is not available in the literature. At higher energies (i.e. 1.5 GeV/nucl. and 2 GeV/nucl.) RQMD and QMD give different results in respect to the time evolution of the phase space, for example for the directed transverse flow. These differences show that consequences of a covariant description of heavy ion reactions within the framework of RQMD are existing even at intermediate energies.

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arXiv1994

A Resonance Model for pi N -> Y K and pi Delta -> Y K Reactions for Kaon Production in Heavy Ion Collisions

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.

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arXiv1994

The Role of the $Δ(1920)$ Resonance for Kaon Production in Heavy Ion Collisions

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

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arXiv1994

Resonance Model of $πΔ\rightarrow Y K$ for Kaon Production in Heavy Ion Collisions

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

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