Effective source sizes of low rapidity soft particle emission

Abstract Correlations of positive pions and protons measured with the Plastic Ball detector in ultrarelativistic nucleus-nucleus collisions are studied. Source parameters are extracted for various projectile-target combinations. While the proton source can be explained by geometry, the pion source shows more subtle effects, which may be related to a very large source component. A comparison with the RQMD model for 200 A GeV 32 S + Au reactions reveals discrepancies for the pion source.