A search for relativistic particles with fractional electric charge at the Cern collider

A search for relativistic particles with fractional electric charge has been performed at the CERN collider using a telescope of scintillation counters to detect particles with abnormally low ionisation. The thickness of the detector (40 gr cm−2) limits this search to particles without strong absorption in matter. No evidence for such particles has been found. This negative result is used to set an upper limit for the ratio of quark yield to that of particles with unit electric charge. For quark masses below 2 GeV/c2 the 90% confidence level upper limits range from 2 × 10−4 to 2.5 × 10−3 depending on the quark mass and elec ric charge.