2-PION BOSE-EINSTEIN CORRELATIONS IN NUCLEAR COLLISIONS AT 200-GEV PER NUCLEON

Results of a pion interferometry analysis are presented for the reacti ons S+C, S+S, S+Cu, S+Ag, S+Au and O+Au at 200 GeV per nucleon. Correl ation functions were measured for pairs of negative pions in narrow wi ndows of transverse momentum and rapidity, as a function of the three components of the momentum difference vector in cylindrical coordinate s. The measured two-pion correlation functions suggest a space-time ev olution of the system which proceeds in the following way for central nucleus-nucleus collisions. After interpretation of the incident nucle i, the pion source expands in a boost invariant way along the collisio n axis. Estimates for the proper time interval between the onset of ex pansion and pion decoupling, as well as for the duration of pion emiss ion are approximately 4 fm/c and < 2 fm/c, respectively. The k(T) depe ndence observed for R(S) is consistent with the effect of resonance de cays, alone or combined with slow transverse expansion. A linear depen dence of the decoupling volume on the multiplicity is observed and ind icates pion decoupling at a constant particle density. Presently avail able model predictions are briefly discussed.