Entropy in nuclear collisions

Data on the multiplicity of pions produced in nucleon-nucleon interactions and central collisions of identical nuclei are discussed using a statistical approach. It is argued that the suppression of the pion production observed at low energies (pLAB < 15 GeV/c per nucleon) is due to entropy transfer to baryons. The enhancement of the entropy production in central S + S collisions at 200 GeV/c per nucleon may be interpreted as manifestation of the increase, by a factor of about 3, of the effective number of degrees of freedom in the early stage of the collision. (orig.)