Energy and centrality dependence of anti-p and p production and the anti-Lambda/anti-p ratio in Pb+Pb collisions between 20 A GeV and 158 A GeV

The transverse mass mt 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 <mt> derived from the mt 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 mt distributions of [overline p] and p are very similar. The ratios of the particle yields, [overline p]/p and [overline Lambda ]/[overline p], are also analyzed. The [overline p]/p ratio exhibits an increase with decreasing centrality and a steep rise with increasing beam energy. The [overline Lambda ]/[overline p] ratio increases beyond unity with decreasing beam energy