Collective motion in nucleus-nucleus collisions at 800 MeV/nucleon

Semi-central Ar+KCl, La+La, and Ar+Pb collisions at 800 MeV/nucleon were studied using the Bevalac Streamer Chamber facility. The results are analysed in the framework of the transverse momentum analysis and in terms of the average sphericity matrix. A critical examination of the analysis procedures, both experimental and theoretical, is given. New procedures are described to account for overall momentum conservation in the reaction, and to correct for azimuthal variations in the detection efficiency. Average transverse momenta per nucleon in the reaction plane are presented for deuterons emitted in the forward hemisphere, that provide the most reliable information. A VUU calculation with a stiff equation of state gives a good fit to the momenta in the Ar+Pb reaction. Flow effects parametrized further using the sphericity tensor, are found stronger than in the cascade model and consistently weaker than predicted by hydrodynamics. Parameters from the sphericity tensor exhibit a larger variation as a function of multiplicity than do the average momenta per nucleon. (orig.)