Decay anisotropy of e+e− sources from pN and pd collisions

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 behaviour for the ratio of the lepton yield from pd to pp reactions as observed at the BEVALAC.