Multiplicity dependence of the pion source in S + A collisions at the CERN SPS

Abstract

The emission of pions from relativistic heavy-ion collisions of S + S, S + Ag and S + Pb at 200 GeV/nucleon is characterized using two-particle interferometry. The multiplicity dependence of the pion source parameters near mid-rapidity is studied. The transversal and longitudinal source parameters, $R_t$ and $R_l$, show a clear increase with the particle multiplicity. The multiplicity dependence is weaker than that expected from a simple model of a freeze-out at a constant density. % The transversal and longitudinal source parameters $R_t$ and $R_l$, show % a clear increase with the particle multiplicity, consistent with the model % of freeze-out at a constant density