Thermalization temperature in Pb+Pb collisions at SpS energy from hadron yields and midrapidity pt distributions of hadrons and direct photons

Abstract

In the frame of 2+1 Bjorken hydrodynamics we describe simultaneously hadron yields and midrapidity pt distributions of direct photons, unflavored, and strange hadrons measured in Pb+Pb collisions at SpS. We find, that a reasonably quantitative description of these data is possible only if we introduce some radial velocity at the beginning of the one-fluid hydrodynamic stage. We fix uniquely all parameters of this model, and estimate an initial temperature of the just thermalized state T_{in}=(200 +40 -20) MeV in the case of EoS with phase transition to Quark-Gluon Plasma, and T_{in}=(230 +60 -30) MeV in the pure hadronic scenario. We conclude that SpS data considered in our study can not distinguish between a production of QGP, and its absence.

Comments: 4 pages, 4 figures, ref. to recent works added