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

TL;DR

This paper presents a geometrical superposition model explaining strangeness production in heavy-ion collisions as a combination of core and corona contributions, clarifying the centrality dependence and addressing strangeness saturation issues.

Contribution

It introduces a superposition model of core and corona emissions to explain strangeness enhancement, linking it to collision geometry and centrality in heavy-ion collisions.

Findings

The model accounts for phi meson and strange particle enhancement with centrality.

Strangeness enhancement is mainly a geometrical effect related to core-corona ratio.

Canonical suppression in the core affects only very peripheral collisions.

Abstract

It is shown that data on strange particle production as a function of centrality in Au-Au collisions at \sqrt(s)_{NN}= 200 GeV can be explained with a superposition of emission from a hadron gas at full chemical equilibrium (core) and from nucleon-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 $\gs$. 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.