Baryon number transport in high-energy nuclear collisions

Abstract

Recent SPS data on the rapidity distribution of protons in p+S, p+Au and S+S collisions at 200 AGeV and preliminary Pb+Pb collisions at 160 AGeV are compared to HIJING and VENUS calculations as well as to predictions based on the Multi-Chain Model (MCM). The preliminary Pb data suggest that a linear dependence of the proton rapidity shift as a function of the nuclear thickness, as first observed in p+A reactions, may apply up to Pb+Pb reactions. The observed rapidity dependence of produced hyperons in both p+A and A+A reactions however cannot be explained in terms of such models without introducing additional non-linear effects.

Baryon junction stopping at the SPS and RHIC via HIJING/B

“…The parameters of this mechanism are adjusted from pA and suffice to reproduce the AA data. We emphasize that the analytic one parameter Multi-Chain-Model [4] also reproduces well [3] the valence proton distributions based on fitting pA. The advantage of a Monte Carlo event generator is the ability to test via other observables such as hyperon production and p ⊥ systematics the consistency of specific dynamical assumptions with a wide range of data.…”

“…Baryon stopping refers to the transport 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 [2,3], recent 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.…”

Baryon junction loops and the baryon-meson anomaly at high energies

“…This central valley could be used as an indicator for partonic processes [63], [64]. Microscopically, the baryon number transport over 4-5 units of rapidity to the equilibrated midrapidity region is not only due to hard processes acting on single valence (di)quark that are described by perturbative QCD, since this yields insufficient stopping [40], [41]. Instead, additional processes such as the nonperturbative junction mechanism as implemented in HIJING/B B v2.0 are able to reproduce the observed distribution.…”

“…One important feature of HIJING is that it can account for the pion quenching component of the baryon anomaly. However, the LUND JETSET diquark string fragmentation mechanism used in HIJING v1.37 [38] completely fails to describe the baryon spectra observed in A+A collisions at all energies [40][41][42]. HIJING/B B1.10 was developed to address this failure at SPS energies.…”

Baryon number transport via gluonic junctions

“…Recent data [1][2][3][4][5] on p + A and A + B interactions at the CERN SPS has revealed a large degree of stopping and strange hyperon production in the heavy nuclear systems. The stopping is significantly under-predicted by models which assume that the primary mechanism for baryon transport is diquark-quark (qq − q) hadronic strings [6,7]. In this letter we implement a variant [8] of the baryon junction mechanism [9,10] to address this problem.…”