Centrality dependence of strangeness production in heavy-ion collisions as a geometrical effect of core-corona superposition

It is shown that data on strange particle production as a function of centrality at Au-Au collision, at root sNN = 200 GeV can be explained with a superposition of emission from a hadron gas at full chemical equilibrium (core) and from nucleon similar to nucleon collisions at the boundary (corona) of the overlapping region of the two colliding nuclei. This model nicely accounts for the enhancement of phi meson and strange particle production as a function of centrality observed in relativistic heavy ion collisions at that energy. The enhancement is mainly a geometrical effect. that is the increasing weight of the core with respect to corona for higher centrality, while strangeness canonical Suppression in the core seems to play a role only in very peripheral collisions. This model. if confirmed at lower energy, would settle the long-standing problem of strangeness under-Saturation in relativistic heavy ion collisions, parametrized by gamma s. Furthermore, it would give a unique tool to locate the onset of deconfinement in nuclear collisions both as a function of energy and centrality if this is to be associated to the onset of the formation of a fully equilibrated core. (C) 2009 Elsevier B.V. All rights reserved.