One-, Two- and Three-Particle Distributions from 158 A GeV/c Central Pb+Pb Collisions

Several hadronic observables have been studied in central 158 A GeV Pb+Pb collisions using data measured by the WA98 experiment at CERN: single negative pion and kaon production, as well as two- and three-pion interferometry. The Wiedemann-Heinz hydrodynamical model has been fitted to the pion spectrum, giving an estimate of the temperature and transverse flow velocity. Bose-Einstein correlations between two identified negative pions have been analysed as a function of kT, using two different parameterizations. The results indicate that the source does not have a strictly boost invariant expansion or spend time in a long-lived intermediate phase. A comparison between data and a hydrodynamical based simulation shows very good agreement for the radii parameters as a function of kT. The pion phase-space density at freeze-out has been measured and agrees well with the Tomasik-Heinz model. A large pion chemical potential close to the condensation limit of the pion mass seems to be excluded. The three-pion Bose-Einstein interferometry shows a substantial contribution of the genuine three-pion correlation, but not quite as large as expected for a fully chaotic and symmetric source.