System-size dependence of strangeness production in nucleus-nucleus   collisions at sqrt{s_{NN}}=17.3 GeV
  Emission of pi, K, phi and Lambda was measured in near-central C+C and Si+Si collisions at 158 AGeV beam energy. Together with earlier data for p+p, S+S and Pb+Pb, the system-size dependence of relative strangeness production in nucleus-nucleus collisions is obtained. Its fast rise and the saturation observed at about 60 participating nucleons can be understood as onset of the formation of coherent partonic subsystems of increasing size. 
NA49 collaboration : C. Alt, et al