A theoretical description of long-range correlations between observables measured in separated rapidity intervals is given. It is shown that, in contrast to two-particle correlations-specifically, correlations between the transverse momenta of charged particles produced in different rapidity intervals-the correlations between the average transverse momenta of all particles in an event that are produced in two rapidity intervals do not tend to zero with increasing number of strings. The energy dependence of the correlations is analyzed. At a fixed degree of collision centrality, the correlations are found to grow upon going over from the SPS energy to the RHIC and LHC energies; they are compared with correlations of the pt-n type. Correlation functions calculated for the minimum-bias case (that is, without any selection in the degree of collision centrality) are contrasted against relevant experimental data on PbPb collisions at the SPS energies. © 2007 Pleiades Publishing, Ltd.