Search for Fractionally Charged Particles

A search was made for fractionally charged particles produced by 12-GeV electrons incident on a copper target. No such particles were detected. Comparison with calculations on photoproduction of pairs of these particles enable lower limits to be placed on the masses of such particles if they exist. Particles of the type discussed in this paper (pure spin-½ Dirac particles with no strong interactions) do not exist with masses below these limits. These limits are dependent on the charge and lifetime assigned to the particle. For lifetimes ≥${10}^{-7\mathrm{}}$ sec, the lower limit varies from 0.2 GeV for $0.04e$ charge, to 1.5 GeV for $0.7e$ charge. For lifetimes ≥${10}^{-8\mathrm{}}$ sec and $0.7e$ charge, the lower limit is 1.1 GeV.