Dielectron production in PP and PD collisions at 1.0 and 4.9 GeV

A satisfactory understanding of dilepton production in nucleon‐nucleoncollisions is a prerequisite for the interpretation of their production in relativistic heavy‐ion collisions. The Dilepton Spectrometer collaboration (DLS) has measured pp,pd→e+,e−X at Tbeam=1.0 and 4.9 GeV, complementing previous p+Be and Ca+Ca measurements by the DLS. The relative yield‐ (pd/pp) is approximately two at both energies, which disagrees significantly with previous expectations.