Hadronic expansion dynamics in central Pb+Pb collisions at 158 GeV per nucleon

Two-particle correlation functions of negative hadrons over wide phase space, and transverse mass spectra of negative hadrons and deuterons near mid-rapidity have been measured in central Pb+Pb collisions at 158 GeV per nucleon by the NA49 experiment at the CERN SPS. A novel Coulomb correction procedure for the negative two-particle correlations is employed making use of the measured oppositely charged particle correlation. Within an expanding source scenario these results are used to extract the dynamic characteristics of the hadronic source, resolving the ambiguities between the temperature and transverse expansion velocity of the source, that are unavoidable when single and two particle spectra are analysed separately. The source shape, the total duration of the source expansion, the duration of particle emission, the freeze-out temperature and the longitudinal and transverse expansion velocities are deduced

Directed and elliptic flow in 158GeV/nucleon Pb+Pb collisions

The directed and elliptic flow of protons and charged pions has been observed from the semicentral collisions of a 158 GeV/nucleon Ph beam with a Pb target. The rapidity and transverse momentum dependence of the flow has been measured. The directed flow of the pions is opposite to that of the protons but both exhibit negative flow at low p(t). The elliptic flow of both is fairly independent of rapidity but rises with p(t)

Deuteron production in central Pb plus Pb collisions at 158A GeV

Experimental results on deuteron emission from central Pb + Pb collisions (E-beam = 158A GeV, fixed target), obtained by NA49 at the CERN SPS accelerator, are presented. The transverse mass in, distribution was measured near mid-rapidity (2.0 < y < 2.5) in the range of 0 < m(t) - m(0) < 0.9 GeV/c(2) (0 < p(t) < 2.0 GeV/c) for the 4% most central collisions. An exponential fit gives an inverse slope T-d = (450 +/- 30) MeV and a yield dN(d)/dy = 0.34 +/- 0.03. The coalescence factor B-2 (m(t) = m(0))=(3.5 +/- 1.0) . 10(-4) GeV2 and its m(t)-dependence are deter-mined and discussed in terms of a model that includes the collective expansion of the source created in a collision. The derived Gaussian size parameter R-G Of the emission volume is consistent with earlier HBT results on the source of pion emission. (C) 2000 Elsevier Science B.V. All rights reserved

Production of phi-mesons in p + p, p + Pb and central Pb + Pb collisions at E-beam=158 A GeV

Yields and phase space distributions of phi -mesons emitted from p + p (minimum bias trigger), p + Pb (at various centralities) and central Pb + Pb collisions are reported (E-beam = 158 A GeV). The decay phi –> K+K- was used for identification. The phi/pi ratio is found to increase by a factor of 3.0 +/- 0.7 from inelastic p + p to central Pb + Pb. Significant enhancement in this ratio is also observed in subclasses of p + p events (characterized by high charged-particle multiplicity) as well as in the forward hemisphere of central p + Pb collisions. In Pb + Pb no shift or significant broadening of the phi -peak is seen. (C) 2000 Published by Elsevier Science B.V

Spectator nucleons in Pb+Pb collisions at 158 A center dot GeV

The composition of forward-going projectile spectator matter in fixed-target Pb+Pb collisions at 158 A.GeV at the CERN SPS has been studied as a function of centrality. The data were measured with the NA49 veto calorimeter. We observe that forward-going spectator matter in central collisions consists of 9 neutrons, 7 protons, and half a deuteron on average. At large impact parameters most spectator nucleons are bound in fragments. The relative resolution of the average impact parameter derived from the measurement of spectator neutrons is roughly 19% in the range from zero to half maximum impact parameters