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

Two-particle correlations of negative pions as a function of charged partic le multiplicity are studied in Pb+Pb collisions at roots = 17.3GeV per nucl eon using the NA44 experiment at the CERN Super Proton Synchrotron(SPS). We find that the source size parameters increase with the charged particle mu ltiplicity. However the slope of the: source size parameters plotted as a f unction of charged multiplicity is slightly larger at high multiplicity tha n at low multiplicity. The value of lambda is independent of charged multip licity. For Pb+Pb collisions, R-L is larger than R-TS and R-TO for all mult iplicity intervals, whereas these three radius parameters were approximatel y equal in S+Nucleus collisions. The ratios (R-L/R-TS) and (R-L/R-TO) for P b+Pb data show almost no dependence on charged multiplicity. The duration o f pion emission Delta tau is constant at 3.8+/-1.1 fm/c as a function of th e charged multiplicity in Pb+Pb collisions. Effective volume (V) is also ca lculated as V=pi x R-TS(2) x R-L; assuming a cylindrically shaped source. W e found, within the limited statistics, the effective Volume rapidly increa ses at high multiplicity.