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Relativistic transport theory of N, Delta and N* (1440) interacting through sigma, omega and pi mesons.
(1997)

Guangjun Mao
Ludwig Neise
Horst Stöcker
Walter Greiner
Zhuxia Li
 A selfconsistent relativistic integraldi erential equation of the Boltzmann UehlingUhlenbecktype for the N*(1440) resonance is developed based on an effective Lagrangian of baryons interacting through mesons. The closed timepath Green s function technique and semiclassical, quasiparticle and Born approxima tions are employed in the derivation. The nonequilibrium RBUUtype equation for the N*(1440) is consistent with that of nucleon s and delta s which we derived before. Thus, we obtain a set of coupled equations for the N,Delta and N*(1440) distribution functions. All the N (1440)relevant inmedium twobody scattering cross sections within the N,Delta and N*(1440) system are derived from the same effective Lagrangian in addition to the mean field and presented analytically, which can be directly used in the study of relativistic heavyion collisions. The theoreticalprediction of the free pp  pp* (1440) cross section is in good agreement with the experimental data. We calculate the inmedium N+N  N+N* , N* +N  N+N and N*+N  N* +N cross sections in cold nuclear matter up to twice the nuclear matter density. The influence of different choices of the N* N* coupling strengths, which can not be obtained through fitting certain experimental data, are discussed. The results show that the density dependence of predicted inmedium cross sections are sensitive to the N* N* coupling strengths used. An evident density dependence will appear when a large scalar coupling strength of g^(sigma) N*N* is assumed. PACS number(s): 24.10.Cn; 25.70.z; 21.65.+f

"Pressure equilibration" in ultrarelativistic heavy ion collisions
(1997)

Jörg Brachmann
Adrian Dumitru
Christian Spieles
Joachim A. Maruhn
Horst Stöcker
Walter Greiner
 We study the time scale for pressure equilibration in heavy ion collisions at AGS energies within the threefluid hydrodynamical model and a microscopic cascade model (UrQMD). We find that kinetic equilibrium is reached in both models after a time of 5 fm/c (centerofmass time). Thus, observables which are sensitive to the early stage of the reaction differ considerably from the expectations within the instant thermalization scenario (onefluid hydrodynamical model).