Search for highly-interacting, fractionally-charged particles in electron-positron annihilation at 29 GeV☆

Abstract We have searched for relativistic, highly-interacting fractionally-charged particles using the free-quark detector at the e + e − storage ring PEP. No convincing events were seen. For an assumed interaction cross section with matter of 100 times geometric, 90% confidence level upper limits on their production relative to e + e − → μ + μ − are between 0.025 and 0.49 depending on quark mass (up to 13 GeV/ c 2 ) and reaction type. These are the first published limits on the production of fractionally charged particles with interaction cross sections of 100 times geometric or larger.