Blast from the past: Constraints on the dark sector from the BEBC WA66 beam dump experiment

We derive limits on millicharged dark states, as well particles with electric or magnetic dipole moments, from the number of observed forward electron scattering events at Big European Bubble Chamber in 1982 CERN-WA-066 beam dump experiment. The states are produced by 400 GeV proton primarily through decays mesons dump, and lack excess places bounds extending up to masses. These improve all other experiments, particular CHARM II.