Directed and elliptic flow measurements for charged pions and protons are reported as a function of transverse momentum, rapidity, and centrality for 40A and 158A GeV PbϩPb collisions, as recorded by the NA49 detector. Both the standard method of correlating particles with an event plane and the cumulant method of studying multiparticle correlations are used. In the standard method the directed flow is corrected for conservation of momentum. In the cumulant method elliptic flow is reconstructed from genuine four-, six-, and eight-particle correlations, showing the first unequivocal evidence for collective motion in AϩA collisions at SPS energies.
The transverse mass m t distributions for antiprotons are measured at midrapidity for minimum bias Pb+Pb collisions at 158A GeV and for central Pb+Pb collisions at 20A, 30A, 40A, and 80A GeV beam energies in the fixed target experiment NA49 at the CERN SPS. The rapidity density dn/dy, inverse slope parameter T, and mean transverse mass m t derived from the m t distributions are studied as a function of the incident energy and the collision centrality and compared to the relevant data on proton production. The shapes of the m t distributions ofp and p are very similar. The ratios of the particle yields,p/p and¯ /p, are also analyzed. Thep/p ratio exhibits an increase with decreasing centrality and a steep rise with increasing beam energy. The¯ /p ratio increases beyond unity with decreasing beam energy.
Results are presented on event-by-event fluctuations in transverse momentum of charged particles, produced at forward rapidities in p + p, C + C, Si+ Si, and Pb+ Pb collisions at 158 AGeV. Three different characteristics are discussed: the average transverse momentum of the event, the ⌽ p T fluctuation measure, and two-particle transverse momentum correlations. In the kinematic region explored, the dynamical fluctuations are found to be small. However, a significant system size dependence of ⌽ p T is observed, with the largest value measured in peripheral Pb+ Pb interactions. The data are compared with predictions of several models.
The transverse mass m t distributions for deuterons and protons are measured in Pb+ Pb reactions near midrapidity and in the range 0 Ͻ m t − m Ͻ 1.0 ͑1.5͒ GeV/ c 2 for minimum bias collisions at 158A GeV and for central collisions at 40 and 80 A GeV beam energies. The rapidity density dn / dy, inverse slope parameter T and mean transverse mass ͗m t ͘ derived from m t distributions as well as the coalescence parameter B 2 are studied as a function of the incident energy and the collision centrality. The deuteron m t spectra are significantly harder than those of protons, especially in central collisions. The coalescence factor B 2 shows three systematic trends. First, it decreases strongly with increasing centrality reflecting an enlargement of the deuteron coalescence volume in central Pb+ Pb collisions. Second, it increases with m t . Finally, B 2 shows an increase with decreasing incident beam energy even within the SPS energy range. The results are discussed and compared to the predictions of models that include the collective expansion of the source created in Pb+ Pb collisions.
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