Baryon Junction Stopping ate the SPS and RHIC via HIJING/B

摘要

The systematic study of baryon stoppin and hyperon production in pp,pA, and AA collisions is essential in order to differentiate the sought after new physics of dense equilibrated matter from non-equilibrium multi-particle production dynamics~1. Baryon stopping refers to the transprot of baryon number in rapidity space away from the nuclear fragmentation regions and is measured through the single inclusive rapidity distribution of protons and hyperons. As discussed in two papers~2,3, recnet SPS data shows a high degree of baryon stopping and anomalous hyperon production. These findings are based on comparisons of predictions using the HIJING~5 and VENUS~6 Monte Carlo event generators with SPS data for p+A and A + B collisions. In particular, the baryon stopping mechanism modeled in HIJING was found to under-estimate the stopping in heavy nuclear collisions, while VENUS model was able to reproduce the baryon stopping and strange baryon production by introducing a new non-equilibrium dynamical mechansm called the double string. The scattering and subsequent hardonization mechanisms is HIJING, adapted from the LUND fritiof~7 and dual parton mdoel (DPM)~8, involves diquark-quark string excitations (see Fig 1a) followed by string breaking. The final valence baryons in this model always emerge within about a unit of rapidity from those of the unbroken diquarks.