Baryon Transport Dynamics: From P — P to PB — PB Collisions

Abstract

Significant baryon stopping and strange hyperon production in heavy nuclear interactions has been recently observed at the CERN SPS [1,2,3,4,5]. The data is significantly under-predicted by models which use diquark-quark (qq − q) hadronic strings for their primary baryon number transport mechanism [6,7] and has thus generated much interest. We therefore study new baryon number transport mechanisms in order to differentiate non-equilibrium multi-particle production dynamics from any new sought after physics. We begin this study by reviewing two new mechanisms as implemented in the VENUS [8] and in a modified version of the dual parton model (DPM) [9] event generators. We then study a third new [10] mechanism, where the baryon number is specifically transferred via gluonic junctions. This mechanism has been implemented in the Monte Carlo event generator, HIJING/B[11], a new version of the HIJING model[12]. W e show that this gluonic mechanism can account for the observed large mid-rapidity valence baryon distribution at the SPS and predicts high baryon densities at RHIC. The highly enhanced hyperon yield and transverse momentum flow observed in PbPb collisions at the SPS can, however, only be partially reproduced by this model.