Collective dynamics in highly relativistic heavy-ion collisions

Abstract

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. pi, K, N, Phi, Lambda, 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 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 <vT> 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 case of thermalization and hydrodynamical expansion, the mean transverse momentum <pT> increases linearly with the hadron mass. In contrast, the string model FRITIOF7.02, which does not account for rescattering of secondary hadrons, predicts a strong dependence of <pT> on the quark composition of the hadron. Due to 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.Comment: 30 pages, REVTEX, 8 eps-figures, results unchanged, however, major revision of parts of the manuscript and some of the figure

Inverse slope systematics in high-energy p+p and Au+Au reactions

“…Note that for an isentropic hydrodynamical expansion dE T /dy decreases with time. On the hadronization hypersurface, we obtain dE T /dy = 640 GeV [18].…”

“…e.g. [18]. At the higher center of mass energy of RHIC, the parton density in the central region increases, and therefore a smaller thermalization time is expected, cf.…”

“…Cylindrically symmetric transverse expansion [18,24,25] For T < T C we assume an ideal hadron gas that includes the complete hadronic spectrum up to a mass of 2 GeV. At T = T C we require that both pressures are equal, which fixes the bag constant to B = 380 MeV/fm 3 .…”

“…also the discussion of p T D in refs. [18,27], and [28] for the effect of c-quark energy loss on lepton radiation in ultrarelativistic heavy-ion collisions).…”

QGP theory: Status and perspectives

“…[19,20]) is ideally suited for the QGP and hydrodynamic expansion reaction phase, but breaks down in the later, dilute, stages of the reaction when the mean free paths of the hadrons become large and flavor degrees of freedom are important. The reach of NFD can also be extended by combining it with a microscopic hadronic cascade model -this kind of hybrid approach (dubbed hydro plus micro) was pioneered in [21] and has been now also taken up by other groups [22].…”