COLLECTIVE MOTION IN AR+PB COLLISIONS AT BEAM ENERGIES BETWEEN 400 AND 1800 MEV NUCLEON

The energy dependence of rapidity distributions and flow effects was studied in central Ar + Pb collisions at 400, 800, and 1800 MeV/nucleon using a streamer chamber. Rapidity distributions for protons and pions are found to have a Gaussian shape whereas those for deuterons exhibit a two-peak structure at the two higher energies. The average in-plane transverse momentum per nucleon and per event shows saturation of flow around 800 MeV/nucleon for this asymmetric system. The aspect ratio of the sphericity tensor is closely correlated with the flow angle. This correlation appears to be independent of beam energy. The number of participating nucleons in central collisions varies from 213 at 400 to 135 at 1800 MeV/nucleon indicating that at the lowest energy almost the entire target nucleus participates in the collision.