Eur. Phys. J. A (2000) 8: 549-552
https://doi.org/10.1007/s100500070077

The directed flow maximum near c_s = 0

¹ Institut für Theoretische Physik der J.W., Goethe-Universität, Postfach 111932, D-60054, Frankfurt am Main, Germany
² Physics Department, Columbia University, 704 Pupin Hall, 538W 120th Street, New York, NY, 10027, USA

^* e-mail: dumitru@nt3.phys.columbia.edu

Received: 7 May 2000
Published online: 15 August 2000

Abstract

We investigate the excitation function of quark-gluon plasma formation and of directed in-plane flow of nucleons in the energy range of the BNL-AGS and for the E _Lab ^kin = 40AGeV Pb + Pb collisions performed recently at the CERN-SPS. We employ the three-fluid model with dynamical unification of kinetically equilibrated fluid elements. Within our model with first-order phase transition at high density, droplets of QGP coexisting with hadronic matter are produced already at BNL-AGS energies, E _Lab ^kin ≃ 10AGeV. A substantial decrease of the isentropic velocity of sound, however, requires higher energies, E _Lab ^kin ≃ 0AGeV. We show the effect on the flow of nucleons in the reaction plane. According to our model calculations, kinematic requirements and EoS effects work hand-in-hand at E _Lab ^kin = 40AGeV to allow the observation of the dropping velocity of sound via an increase of the directed flow around midrapidity as compared to top BNL-AGS energy.