2 research outputs found
Longitudinal fluid dynamics for ultrarelativistic heavy-ion collisions
We develop a 1+1 dimensional hydrodynamical model for central heavy-ion
collisions at ultrarelativistic energies. Deviations from Bjorken's scaling are
taken into account by implementing finite-size profiles for the initial energy
density. The calculated rapidity distributions of pions, kaons and antiprotons
in central Au+Au collisions at the c.m. energy 200 AGeV are compared with
experimental data of the BRAHMS Collaboration. The sensitivity of the results
to the choice of the equation of state, the parameters of initial state and the
freeze-out conditions is investigated. Experimental constraints on the total
energy of produced particles are used to reduce the number of model parameters.
The best fits of experimental data are obtained for soft equations of state and
Gaussian-like initial profiles of the energy density. It is found that initial
energy densities required for fitting experimental data decrease with
increasing critical temperature of the phase transition.Comment: 22 pages, 8 figures; 4 figures and 12 references adde
Temperature dependent sound velocity in hydrodynamic equations for relativistic heavy-ion collisions
We analyze the effects of different forms of the sound-velocity function
cs(T) on the hydrodynamic evolution of matter formed in the central region of
relativistic heavy-ion collisions. At high temperatures (above the critical
temperature Tc) the sound velocity is calculated from the recent lattice
simulations of QCD, while in the low temperature region it is obtained from the
hadron gas model. In the intermediate region we use different interpolations
characterized by the values of the sound velocity at the local maximum (at T =
0.4 Tc) and local minimum (at T = Tc). In all considered cases the temperature
dependent sound velocity functions yield the entropy density, which is
consistent with the lattice QCD simulations at high temperature. Our
calculations show that the presence of a distinct minimum of the sound velocity
leads to a very long (about 20 fm/c) evolution time of the system, which is not
compatible with the recent estimates based on the HBT interferometry. Hence, we
conclude that the hydrodynamic description is favored in the case where the
cross-over phase transition renders the smooth sound velocity function with a
possible shallow minimum at Tc.Comment: 6 pages, 3 figures, talk given at SQM'07 Levoca, Slovaki