Equation of state of nucleonic matter

Abstract

The nuclear equation of state (EoS) is investigated by flow phenomena in relativistic heavy-ion collisions, both in transverse and radial direction, in comparison to experimental data from 150 A MeV to 11 A GeV. To this aim the collective dynamics of the nucleus-nucleus collision is described within a transport model of the coupled channel RBUU type. There are two factors which dominantly determine the baryon flow at these energies: the momentum dependence of the scalar ($U_S$) and vector potentials ($U_μ$) for baryons and the resonance/string degrees of freedom for energetic hadron excitations. We fix the explicit momentum dependence of the nucleon-meson couplings by the nucleon optical potential up to 1 GeV and extrapolate to higher energy. When assuming the optical potential to vanish identically for $E_{kin} \geq 3.5$ GeV we simultaneously describe the sideward flow data of the PLASTIC BALL, FOPI, EoS and E877 collaborations, the elliptic flow data of the E895 and E877 collaborations and approximately the rapidity and transverse mass distribution of protons at AGS energies without employing any {\it explicit} assumption on a phase transition in the EoS. However, the gradual change from hadronic to string degrees of freedom with increasing bombarding energy can be viewed as a transition from {\it hadronic} to {\it string} matter, i.e. a dissolution of hadrons at high energy density.