Strangeness dynamics in relativistic nucleus-nucleus collision

Abstract

We investigate hadron production as well as transverse hadron spectra in nucleus-nucleus collisions from 2 $A\cdot$GeV to 21.3 $A\cdot$TeV within two independent transport approaches (UrQMD and HSD) that are based on quark, diquark, string and hadronic degrees of freedom. The comparison to experimental data demonstrates that both approaches agree quite well with each other and with the experimental data on hadron production. The enhancement of pion production in central Au+Au (Pb+Pb) collisions relative to scaled $pp$ collisions (the 'kink') is well described by both approaches without involving any phase transition. However, the maximum in the $K^{+}/{\pi }^{+}$ ratio at 20 to 30 A$\cdot$GeV (the 'horn') is missed by $\sim$ 40%. A comparison to the transverse mass spectra from $pp$ and C+C (or Si+Si) reactions shows the reliability of the transport models for light systems. For central Au+Au (Pb+Pb) collisions at bombarding energies above $\sim$ 5 A$\cdot$GeV, however, the measured $K^{\pm }$ $m_T$-spectra have a larger inverse slope parameter than expected from the calculations. The approximately constant slope of $K^{\pm }$ spectra at SPS (the 'step') is not reproduced either. Thus the pressure generated by hadronic interactions in the transport models above $\sim$ 5 A$\cdot$GeV is lower than observed in the experimental data. This finding suggests that the additional pressure - as expected from lattice QCD calculations at finite quark chemical potential and temperature - might be generated by strong interactions in the early pre-hadronic/partonic phase of central Au+Au (Pb+Pb) collisions.

10 pages, 5 figures, Invited talk presented by H. Stocker at ERICE-2003 (Sep. 2003, Erice, Italy), to be published in Prog. Part. Nucl. Phys. 52 (2004)

References in corpus (8)

• Why does the Quark-Gluon Plasma at RHIC behave as a nearly ideal fluid ?
• Charged Pion Production in 2 to 8 AGeV Central Au+Au Collisions
• Transverse Activity of Kaons and the Deconfinement Phase Transition in Nucleus--Nucleus Collisions
• Evidence for nonhadronic degrees of freedom in the transverse mass spectra of kaons from relativistic nucleus-nucleus collisions?
• Strangeness from 20 AGeV to 158 AGeV
• Energy Scan Program at the Cern SPS and An Observation of the Deconfinement Phase Transition in Nucleus--Nucleus Collisions
• Dynamics of strange, charm and high momentum hadrons in relativistic nucleus-nucleus collisions
• System size dependence of strangeness production at 158 GeV/n

Cited by in corpus (10)

• Particle Number Fluctuations in High Energy Nucleus-Nucleus Collisions from Microscopic Transport Approaches
• Fluctuations of the $K/\pi$ Ratio in Nucleus-Nucleus Collisions: Statistical and Transport Models
• On the chemical equilibration of strangeness-exchange reaction in heavy-ion collisions
• Baryon Number and Electric Charge Fluctuations in Pb+Pb Collisions at SPS energies
• Multiplicity Fluctuations in Nucleus-Nucleus Collisions: Dependence on Energy and Atomic Number
• Multiplicity Fluctuations in Au+Au Collisions at RHIC
• Dynamics of strange, charm and high momentum hadrons in relativistic nucleus-nucleus collisions
• Computation of pion and kaon heavy ion multiplicities in a gluon-meson model
• Web-page on UrQMD Model Validation
• Open and Hidden Strangeness Production in Nucleon-Nucleon Collisions