The width of the rapidity distribution in heavy ion collisions

We have studied the widths of the rapidity distributions of particles produced in nucleus-nucleus collisions at various center of mass energies and as a function of centrality at SPS energies. We show that the width of the rapidity distribution is sensitive to longitudinal flow, velocity of sound in the medium, and rescattering of particles. We explore the possibility of distinguishing the initial hard scattering regime from final state effects by studying the variation in the width of the rapidity distribution of the particles with centrality for various pT values.