ar X iv : h ep - p h / 05 01 17 9 v 1 1 9 Ja n 20 05 MULTIPLICITY AND p t CORRELATIONS IN RELATIVISTIC NUCLEAR COLLISIONS

The theoretical description of the correlations between observables in two separated rapidity intervals for AA-interactions at high energies is presented. In the case with the real nucleon distribution density of colliding nuclei the MC calculations of the long-range correlation functions at different values of impact parameter are done. For n–n and p t –n correlations it is shown that the impact parameter fluctuations at a level of a few fermi, unavoidable in the experiment, significantly change the magnitude of correlation coefficients. The rise of p t –n and especially p t –p t correlation coefficients is found when one passes from SPS to RHIC and LHC energies. The colour string model [1, 2] originating from Gribov-Regge approach is being widely applied for the description of the soft part of the multiparticle production in hadronic and nuclear interactions at high energies. In this model at first stage of hadronic interaction the formation of the extended objects-the quark-gluon strings-takes place. At second stage the hadronization of these strings produces the observed hadrons. In the original version the strings evolve independently and the observed spectra are just the sum of individual string spectra. However in the case of nuclear collision, with growing energy and atomic number of colliding nuclei, the number of strings grows and one has to take into account the interaction between them. One of possible approaches to the problem is the colour string fusion model [3]. The model is based on a simple observation that due to final transverse dimensions of strings they inevitably have to start to overlap with the rise of their density in transverse plane. At that the interaction of string colour fields takes place, which changes the process of their fragmentation into hadrons as compared with the fragmentation of independent strings. So we have one more interesting nonlinear phenomenon in nuclear interactions at high energies-the field of physics the investigations in which were initiated by pioneer works of academician A.M. Baldin [4]. It was shown [3, 5, 6] that the string fusion phenomenon considerably damps the charged particle multiplicity and simultaneously increase their mean p t value as compared with the case of independent strings. In accordance with a general Schwinger idea [7] and the following papers [8, 9] (colour ropes model) two possible versions of string fusion mechanism were suggested. The first version [5] of the model assumes that the colour fields are summing up …