Semi-hard scatterings at RHIC and LHC: initial conditions and charged multiplicities

Abstract

Minijet production in ultra-relativistic heavy-ion collisions is discussed by taking semi-hard parton rescatterings explicitly into account. At both RHIC and LHC energies we find sizable effects on global characteristics of the nuclear collision like the initial multiplicity and transverse energy of the minijets. The dependence of these quantities on the cutoff that separates soft and hard interactions becomes much smoother after the inclusion of the rescatterings. This allows to define an energy and centrality dependent saturation cutoff and to push perturbative computations to rather low values of the cutoff. As an application we compute the charged multiplicity at mid rapidity and compare it to the recent RHIC data.