COLLECTIVE FLOW OF PIONS IN RELATIVISTIC HEAVY-ION COLLISIONS

The transverse-momentum distributions of pions in the Au(1 GeV/nucleon ) + Au collisions are analyzed. The calculations are carried out withi n relativistic mean-field one- and two-fluid models. The rapidity dist ributions of the mean transverse momentum of pions are found to be fai rly sensitive to the nuclear equation of state and, especially, to the stopping power. It is shown that the collective flow of pions in the reaction plane always correlates with the ''hot'' how of nucleons (i.e . those emitted from hot regions of nuclear system), while not always with the total nucleon how. This ''hot'' nucleon flow can be experimen tally singled out by selecting nucleons with sufficiently high transve rse momenta. We predict that the ''hot'' nucleon flow selected in this way will always correlate with the pion flow. Available experimental data on transverse-momentum spectra of pions are compared with calcula tions employing various equations of state and stopping power.