Abstract
It is shown that data on strange particle production as a function of centrality in Au–Au collisions at sNN=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 ϕ 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 γS. 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.
Highlights
One of the observed features of hadron production in relativistic heavy ion collisions is the deviation from full chemical equilibrium of particles containing strange constituent quarks
Since strangeness production is suppressed in NN collisions with respect to a fully equilibrated hadron gas, while temperature is almost the same [7, 8]), if such single NN collisions accounts for a significant fraction of total particle production, a global fit to one hadron-resonance gas would find γS significantly less than 1
Finding [13] that strangeness enhancement from N = 200 GeV can be well described by a model peripheral to central relativistic where particle production arises from two sources: a fully equilibrated core at a temperature of ∼ 160 MeV as in the statistical model and an outer region of single NN collisions, called corona
Summary
One of the observed features of hadron production in relativistic heavy ion collisions is the deviation from full chemical equilibrium of particles containing strange constituent quarks. [6], the authors assume that a string percolation process gives rise to a large cluster in the core of the nuclear overlapping region and smaller clusters in the outer region ( referred to as corona), eventually decaying into hadrons according to the statistical model ansatz With this core-corona superposition scheme, and assuming γS = 1 the authors could reproduce the centrality dependence of K/π ratio at SPS and RHIC because small corona clusters suffer the so-called canonical suppression effect. More detailed analysis found out that the rapidity densities of various hadron species as a function of centrality in Au-Au collisions at 200A GeVat RHIC as well as nuclear modification factors are well described with the EPOS model in a core-corona scheme[10] It has been taken into account for analysis of J/ψ production within the statistical hadronization model [11]. The basic ideas and conclusions discussed here have been reported earlier in ref. [13]; in this work, we expand, explain and update our analysis
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