Energy and centrality dependence of $\overline{p}$ and $p$ production and the $\overline{\lambda}/\overline{p}$ ratio in Pb+Pb collisions between 20A GeV and 158A GeV

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 left angle $\left \langle {m}_{t} \right \rangle$ 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 of $\bar{p}$ and $p$ are very similar. The ratios of the particle yields, $\bar{p}/p$ and $\Lambda/p\bar{p}$, are also analyzed. The $\bar{p}/p$ ratio exhibits an increase with decreasing centrality and a steep rise with increasing beam energy. The $\Lambda/\bar{p}$ ratio increases beyond unity with decreasing beam energy.