Energy and centrality dependence of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mover><mml:mrow><mml:mi>p</mml:mi></mml:mrow><mml:mrow><mml:mrow/><mml:mo>¯</mml:mo></mml:mrow></mml:mover></mml:mrow></mml:math>and<i>p</i>production and the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mover><mml:mrow><mml:mi>Λ</mml:mi></mml:mrow><mml:mrow><mml:mrow/><mml:mo>¯</mml:mo></mml:mrow></mml:mover><mml:mo>/</mml:mo><mml:mover><mml:mrow><mml:mi>p</mml:mi></mml:mrow><mml:mrow><mml:mrow/><mml:mo>¯</mml:mo></mml:mrow></mml:mover></mml:mrow></mml:math>ratio in Pb+Pb collisions between 20<i>A</i>GeV and 158<i>A</i>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 $\mathit{dn}/\mathit{dy}$, inverse slope parameter T, and mean transverse mass $\ensuremath{\langle}{m}_{t}\ensuremath{\rangle}$ 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 $\overline{p}$ and p are very similar. The ratios of the particle yields, $\overline{p}$/p and $\overline{\ensuremath{\Lambda}}$/$\overline{p}$, are also analyzed. The $\overline{p}$/p ratio exhibits an increase with decreasing centrality and a steep rise with increasing beam energy. The $\overline{\ensuremath{\Lambda}}$/$\overline{p}$ ratio increases beyond unity with decreasing beam energy.