Cluster Approach to Intranuclear Cascade for Relativistic Heavy-Ion Collisions

Abstract

A new approach to the intranuclear cascade model for relativistic heavy-ion reactions is presented. The effect of nucleon concentration on the collision process is explicitly included. It is found that the contributions from the nonbinary processes are far from being negligible. Such processes are shown to broaden the angular distribution of inclusive proton spectra for 20 Ne + 238 U head-on collisions.PACS numbers: 25.70.Bc, 24.10.Dp, 25.70.Fg In the last few years, a number of theoretical and experimental studies on relativistic heavyion collisions (RHIC) have been done. The ultimate aim of such investigations is to learn about the properties of nuclear matter at extreme conditions of density and temperature. Up to the present moment, our understanding of this subject is still far from being clear. Most of the available experimental data are inclusive, averaged over all impact parameters. Such data are shown to be unable, in general, to give detailed information about the collision dynamics. Thus they hardly detect any differences among the current models.However, a new type of information is available from recent multiplicity-selected experiments. 1 Stbcker et at? discussed the results of the highmultiplicity-selected Ne(393 MeV/u)+ U reaction (head on) with respect to the predictions of several theoretical models. They claimed that the model based on nuclear fluid dynamics has some advantage in reproducing the side-peaked angular distribution over the conventional intranuclear cascade calculation.Nevertheless, the Monte Carlo approach is useful to simulate the microscopic process, because it furnishes a direct way of calculating microscopic quantities without the introduction of any phenomenological parameter. It still remains to discuss further to what extent the intranuclear cascade model is adequate in simulating the RHIC.The basic point of the conventional cascade calculation is the assumption of sequential binary collisions. 3 However, this is not a trivial assumption. Rigorously speaking, such treatment is justified only in the limit of dilute-gas approximation, where correlations, during the nucleon-nucleon collisions, are negligible. In RHIC, even when the incident energy is high enough so that the nucleon de Broglie wavelength is smaller than the mean nucleon interdistance at the normal nuclear density, we hardly expect that the system behaves as a dilute gas during the whole process. In fact for central collisions of heavy systems, a local density increase due to compression may cause correlations in nucleon-nucleon collisions. Such correlations manifest the nonbinary character of RHIC. These nonbinary correlations are fundamental for the possible appearance of novel collective phenomena, such as hydrodynamic shock waves, pion condensation, and density isomeric states of nuclear matter. Thus it is essential to study the nonbinary correlations in the context of the intranuclear cascade model.In this work, we propose a new approach to the intranuclear cascade process which permits us, in a simple w...

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