System-Size Dependence of Strangeness Production at 158 AGeV

        Strange hadron (K+, K-, phi, Lambda and Antilambda) and pion
        production is measured by the CERN-SPS experiment NA49 at
        158 AGeV in p+p and central C+C, Si+Si and Pb+Pb collisions.
        The relative strangeness production in dependence on the
        system size shows a rapid rise followed by a saturation above
        60 participating nucleons. For these interactions as well as
        for centrality selected Pb+Pb reactions the collision density
        serves as a common scaling parameter indicating that the
        collisions in A+A reactions cannot be independent.

        The formation of partonic clusters provides an intuitive
        explanation for the strangeness enhancement as well as for
        other observables e.g. the fluctuation pattern. The evolution
        of cluster number and size in the percolation picture can be
        connected with the disappearance of canonical strangeness
        suppression in statistical models.

        In the statistical analysis of the NA49 data by Becattini the
        chemical freeze out points of C+C and Si+Si reactions are
        found to be in immediate vicinity of the phase boundary.
        This leaves no room for inelastic hadronic rescattering to
        achieve chemical equilibrium while the radial flow, which is
        consistent with the transverse momentum broadening, creates in
        the framework of blast wave fits an increasing difference
        between chemical and thermal freeze out temperature with the
        system size, providing time for elastic rescattering.