Space-time evolution of the hadronic source in peripheral to central Pb + Pb collisions

Two-particle correlations of negative pions as a function of charged particle multiplicity are studied in Pb+Pb collisions at square root s=17.3 GeV per nucleon using the NA44 experiment at the CERN Super Proton Synchrotron (SPS). We find that the source size parameters increase with the charged particle multiplicity. However the slope of the source size parameters plotted as a function of charged multiplicity is slightly larger at high multiplicity than at low multiplicity. The value of lambda is independent of charged multiplicity. For Pb+Pb collisions, R/sub L/ is larger than R/sub TS/ and R/sub TO/ for all multiplicity intervals, whereas these three radius parameters were approximately equal in S+Nucleus collisions. The ratios (R/sub L//R/sub TS/) and (R/sub L//R/sub TO/) for Pb+Pb data show almost no dependence on charged multiplicity. The duration of pion emission Delta T is constant at 3.8+or-1.1 fm/c as a function of the charged multiplicity in Pb+Pb collisions. The effective volume (V) is also calculated as V= pi *R/sub TS//sup 2/*R/sub L/, assuming a cylindrically shaped source. We found, within the limited statistics, the effective volume rapidly increases at high multiplicity. (23 refs).