Baryon number transfer in nuclear collisions at SPS energies

New data on identified baryons in the projectile hemisphere of p+p and centrality-selected p + Pb and Pb + Pb collisions are shown. Information from pion-induced interactions is used to isolate the projectile role in the observed phenomena. A common picture emerges for p + p, p, + Pb and Pb + Pb reactions: with increasing centrality, the projectile baryon number is strongly "pushed" towards the backward hemisphere of the collision. In the magnitude of this common effect, most central Pb + Pb interactions occupy a medium position between p + p and central p + Pb reactions. (6 refs).