  It has been observed recently that while continuum dilepton production and
open charm production in high-energy $pA$ collisions can be described in terms
of the superposition of $pp$ collisions, dilepton yields in S+U collisions are
in excess of similar extrapolations. This feature can be explained as arising
from the interaction of gluons produced in different soft baryon-baryon
collisions, leading to additional open-charm pairs in nucleus-nucleus
collisions but not in $pA$ collisions.
