Evidence for low freeze-out temperature and large transverse flow in central collisions of.pdf

a r X i v : h e p - p h / 9 6 1 2 3 3 6 v 1 1 2 D e c 1 9 9 6 Preprint FZR–149 September 1996 Evidence for low freeze-out temperature and large transverse flow in central collisions of Pb + Pb at 158 AGeV B. Ka?mpfer Institut fu?r Theoretische Physik, TU Dresden, 01062 Dresden, and Forschungszentrum Rossendorf, PF 510119, 01314 Dresden Utilizing a hydrodynamical model for the freeze-out stage in heavy-ion reactions, we extract from resolved transverse hadron spectra at midrapidity an inverse slope parameter (temperature) TPb = 120 MeV and an averaged transverse flow velocity vaver ⊥Pb = 0.43 c in central collisions of Pb + Pb at 158 AGeV. 1 Recently the (yet preliminary) transverse momentum spectra of π±, π0, K±, K0s , p±, Λ, Λ? at midrapidity, resulting in central collisions of Pb + Pb at beam energy 158 AGeV, have been reported [1, 2, 3]. To analyze these spectra one can utilize a hydrodynamical description of the freeze-out stage. The concept of hydrodynamics for describing heavy-ion collisions has a long history, and quite sophisticated models have been proposed for modeling the hadron dynamics at freeze-out (for a survey cf. [4]). The general interest in hydrodynamics is motivated by the fact that this approach is intimately related to the use of the equation of state of strongly interacting matter. Within such a framework the chiral symmetry restoration or the phase transition from hadron matter to a quark-gluon plasma appear as particularly interesting. It is still one of the ultimate goals in the realm of heavy-ion physics at relativistic energies to search for signals of deconfined matter. Now, it seems that only a combination of various observables can help to pin down information on the state of maximum density and excitation energy. Sometimes penetrating probes, like dileptons and photons, are considered as favorable signals for the diagnostic of the early stage in the course of colliding nuclei. Hadrons, otherwise, carry mainly information on the l