  When a diquark does not fragment directly but breaks in such a way that only
one of its quarks gets into the produced baryon, the latter is produced closer
to mid rapidities. The relative size of this diquark breaking component
increases quite fast with increasing energy. We show that at a given energy it
also increases with the atomic mass number and with the centrality of the
collision and that it allows to explain the rapidity distribution of the net
baryon number ($p$-$\bar{p}$) in $SS$ central collisions. Predictions for
$Pb$-$Pb$ collisions are presented.
