Thermalization in high energy nuclear collisions

Abstract complete events of the symmetric collisions Ca + Ca at E / A = 400 MeV and 1050 MeV and Nb + Nb at E / A = 400 MeV and 650 MeV have been measured with the Plastic Ball/Wall 4π spectrometer. The degree of isotropy expressed by the ratio of the mean transverse to the mean longitudinal momentum in each event is determined as a function of the charged particle multiplicity. Also discussed are proton energy distributions at θ cm = 90° and their multiplicity dependences.