  A full calculation of lepton-pair angular characteristics is carried out for
$e^+e^-$ pairs created in $pp$, $pn$ and $pd$ collisions at intermediate
energies. It is demonstrated that the proposed new observable, the dilepton
decay anisotropy, quite sensitively changes for different sources and may be
useful for their disentangling. The relevance of the dilepton decay anisotropy
is shown in the context of a puzzling energy behavior for the ratio of the
lepton yield from $pd$ to $pp$ reactions as observed at the BEVALAC.

Nuclear Theory