Collective dynamics in highly relativistic heavy-ion collisions

Hydrodynamics with cylindrical symmetry in transverse direction and longitudinal scaling flow is employed to calculate the transverse momentum spectra of various hadrons and clusters (e.g., π, K, N, Φ, Λ, d, He) in central heavy-ion collisions at CERN-SPS and BNL-RHIC energies up to pT=4 GeV. We discuss the sensitivity of these spectra with respect to the initial transverse density profile as well as to the choice of 'freeze-out' hypersurface. For √ (s) =18A GeV (SPS energy) and pT<2 GeV, overall good agreement of the pT distributions with data is found when freeze-out occurs along the T=130 MeV isotherm. Even high-pT neutral pion data can be described for a particular choice of the initial transverse density profile. It is shown that the average transverse velocity left-angle vT right-angle of heavy hadrons and hadronic clusters is a good measure for the collective flow velocity. The latter is found to be rather similar for SPS and RHIC energies, due to the 'stall' of the flow within the long-lived mixed phase at RHIC. In the case of thermalization and hydrodynamical expansion, the mean transverse momentum left-angle pT right-angle increases linearly with the hadron mass. In contrast, the string model FRITIOF 7.02, which does not account for rescattering of secondary hadrons, predicts a strong dependence of left-angle pT right-angle on the quark composition of the hadron. Because of the different sensitivity to hard processes, hadrons with charm (anti)quarks acquire significantly more transverse momentum than hadrons without c (or even without s) quarks. copyright 1999 The American Physical Society