  The yields of (anti-)protons were measured by the NA49 Collaboration in
centrality selected Pb+Pb collisions at 40A GeV and 158A GeV. Particle
identification was obtained in the laboratory momentum range from 5 to 63 GeV/c
by the measurement of the energy loss dE/dx in the TPC detector gas. The
corresponding rapidity coverage extends 1.6 units from mid-rapidity into the
forward hemisphere. Transverse mass spectra, the rapidity dependences of the
average transverse mass, and rapidity density distributions were studied as a
function of collision centrality. The values of the average transverse mass as
well as the midrapidity yields of protons when normalized to the number of
wounded nucleons show only modest centrality dependences. In contrast, the
shape of the rapidity distribution changes significantly with collision
centrality, especially at 40A GeV. The experimental results are compared to
calculations of the HSD and UrQMD transport models.
