Re-Hardening of Hadron Transverse Mass Spectra in Relativistic Heavy-Ion Collisions

We analyze the spectra of pions and protons in heavy-ion collisions at relativistic energies from 2 A GeV to 65+65 A GeV by using a jet-implemented hadron-string cascade model. In this energy region, hadron transverse mass spectra first show softening until SPS energies, and re-hardening may emerge at RHIC energies. Since hadronic matter is expected to show only softening at higher energy densities, this re-hardening of spectra can be interpreted as a good signature of the quark-gluon plasma formation.Comment: 10 pages, 3 figures, 1 table, Poster presentation at QM2001, Revised to correct latex error in citation on April 6, 200

Nonequilibrium models of relativistic heavy-ion collisions

To be published in J. Phys. G - Proceedings of SQM 2004 : We review the results from the various hydrodynamical and transport models on the collective flow observables from AGS to RHIC energies. A critical discussion of the present status of the CERN experiments on hadron collective flow is given. We emphasize the importance of the flow excitation function from 1 to 50 A.GeV: here the hydrodynamic model has predicted the collapse of the v2-flow ~ 10 A.GeV; at 40 A.GeV it has been recently observed by the NA49 collaboration. Since hadronic rescattering models predict much larger flow than observed at this energy we interpret this observation as evidence for a first order phase transition at high baryon density r b. Moreover, the connection of the elliptic flow v2 to jet suppression is examined. It is proven experimentally that the collective flow is not faked by minijet fragmentation. Additionally, detailed transport studies show that the away-side jet suppression can only partially (< 50%) be due to hadronic rescattering. Furthermore, the change in sign of v1, v2 closer to beam rapidity is related to the occurence of a high density first order phase transition in the RHIC data at 62.5, 130 and 200 A.GeV

Mean-field effects on collective flow in high-energy heavy-ion collisions at 2-158A GeV energies

Collective flows in heavy-ion collisions from AGS [(2–11)A GeV] to SPS [(40, 158)A GeV] energies are investigated in a nonequilibrium transport model with the nuclear mean field (MF). Sideward 〈Px〉, directed v1, and elliptic flows v2 are systematically studied with different assumptions for the nuclear equation of state (EOS). We find that the momentum dependence on the nuclear MF is important for the understanding of the proton collective flows at AGS and SPS energies. Calculated results with momentum-dependent MF qualitatively reproduce the experimental data of proton sideward, directed, and elliptic flows in a incident energy range of (2–158)A GeV

Elliptic flow in a hadron-string cascade model at 130 GeV energy

We present the analysis of elliptic flow at √s = 130 A GeV energy in a hadron-string cascade model. We find that the final hadronic yields are qualitatively described. The elliptic flow v2 is reasonably well-described at low transverse momentum (pT < 1 GeV/c) in mid-central collisions. On the other hand, this model does not explain v2 at high pT or in peripheral collisions and thus generally, it underestimates the elliptic flow at RHIC energy