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

Abstract

Two-particle correlations of negative pions as a function of charged particle multiplicity are studied in Pb+Pb collisions at $\sqrt{s}=17.3$ 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, $R_L$ is larger than $R_{TS}$ and $R_{TO}$ for all multiplicity intervals, whereas these three radius parameters were approximately equal in S+Nucleus collisions. The ratios ( $R_L/R_{TS}$ ) and ( $R_L/R_{TO}$ ) for Pb+Pb data show almost no dependence on charged multiplicity. The duration of pion emission $\Delta \tau$ is constant at 3.8 $\pm$ 1.1 fm/c as a function of the charged multiplicity in Pb+Pb collisions. Effective volume (V) is also calculated as V= $\pi\times R_{TS}^2\times R_L$ , assuming a cylindrically shaped source. We found, within the limited statistics, the effective volume rapidly increases at high multiplicity.