A search for free quarks in deep inelastic muon scattering

Abstract A search was made at the CERN SPS for long-lived fractionally charged particles produced in deep inelastic muon interactions on a Be target using the existing muon beam line as a spectrometer. No such particles were found, leading to upper limits for the production cross section of the order of 10 −36 cm 2 for 200 GeV incident muon momentum and quark masses below 9 GeV for the 2 3 charge and 15 GeV for 1 3 charge.