Constraints on string percolation model from anomalous centrality evolution data in Au-Au collisions at sqrt(s_ NN) = 62 and 200 GeV

Abstract

Anomalous centrality evolution of two-particle angular correlations observed in Au-Au collisions at √ sNN = 62 and 200 GeV and the onset of ridge structures are considered in the model of interacting quark-gluon strings. We assume that at the given energy of nucleus-nucleus collisions the critical energy density may be reached at the specific cen trality. In a string percolation model this might be treated equivalently to a formation of a large cluster of strings characterized by the critical string density, with a size comparable to the wh ole area of interaction of two nuclei. This hypothesis allows to define some constraints on the stri ng percolation model using data on transitional centralities in Au-Au collisions at these two energies. Results are extrapolated to the LHC energy where high string densities (exceeding the critical value) are confirmed for all classes of centralities in Pb-Pb collisions. Interaction between strings inside large clusters formed i n nucleus-nucleus collisions is considered in a simplified Monte Carlo model. This model is applied t o the qualitative analysis of the onset of collectivity and the ridge formation in Pb-Pb colli sions. It is shown that the approach of the repulsive string-string interaction is capable to expl ain the appearance of elliptic and triangular flow observed in nucleus-nucleus collisions at RHIC and LHC e nergies.