A new search for relativistic particles with fractional electric charge at the CERN pp collider

Abstract We report on a search for relativistic particles with fractional electric charge at the CERN p p colider, using a telescope of scintillation counters to detect particles with anomalously low ionization. Since no event survives the selection criteria, upper limits on quark production are deduced from this experiment. At 90% confidence level and in the limit of very light quarks with charge ± 1 2 and ± 2 3 they are 2.8×10 −6 and 5.6×10 −5 , respectively, per single charged particle. These limits increase rapidly with increasing quark mass and are nearly two and one order of magnitude better than previously measured by UA2.