Observation of Direct Production of Leptons in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>p</mml:mi></mml:math>-Be Collisions at 300 GeV

Direct production of electrons and muons is observed in 300-GeV $p$-Be collisions. The yields are much higher than predicted from current models. Data are consistent with charge symmetry and universality.