STOPPING AND RADIAL FLOW IN CENTRAL NI-58-58 COLLISIONS BETWEEN 1A AND 2A GEV(NI)

The production of charged pions, protons. and deuterons has been studi ed in central collisions of Ni-58 on Ni-58 at incident beam energies o f 1.06A, 1.45A, and 1.93A GeV. The dependence of transverse-momentum a nd rapidity spectra on the beam energy and on the centrality of the co llison is presented. It is shown that the scaling of the mean rapidity shift of protons established for between 10A and 200A GeV at the Broo khaven AGS and the CERN SPS accelerators energies is valid down to 1A GeV. The degree of nuclear stopping is discussed; quantum molecular dy namics calculations reproduce the measured proton rapidity spectra for the most central events reasonably well, but do not show any sensitiv ity between the soft and the hard equation of state. A radial Bow anal ysis, using the midrapidity transverse-momentum spectra, delivers free ze-out temperatures T and radial flow velocities beta(r) which increas e with beam energy up to 2A GeV; in comparison to the existing data of Au on Au over a large range of energies, only beta(r) shows a system size dependence.