Fluctuations and clustering of multiplicity in collisions of relativistic ions

We discuss the recently measured event-by-event multiplicity fluctuations in relativistic heavy-ion collisions. It is shown that the observed non-monotonic behavior of the scaled variance of the multiplicity distribution as a function of collision centrality can be fully explained by the correlations between produced particles promoting cluster formation (such an effect is not observed in a widely used string-hadronic models of nuclear collisions). We define a cluster as a quasi-neutral gas of charged and neutral particles which exhibits collective behavior. The characteristic space scale of this shielding is the Debye length. The multiplicity distribution in a cluster is given by a negative binomial distribution while the rest (reservoir), treated as a superposition of elementary collisions, is described by a binomial distribution. The ability to generate spatial structures (cluster phase) with self-similar fluctuations of multiplicity sign the propensity to self-organize of hadronic matter