Search for Exclusive Free-Quark Production ine+e−Annihilation

The products of $e^{+}{e}^{-}$ annihilation at 29-GeV center-of-mass energy have been searched for free fractionally charged particles produced in exclusive two-body final states. No evidence for fractionally charged quarks was found and the upper limits on the ratio $R_{q\overline{q}}=\frac{{\sigma }_{q\overline{q}}}{{\sigma }_{\mu \overline{\mu }}}$ are below 1% for quarks with charges $\frac{1}{3}e$ or $\frac{2}{3}e$ and masses below about 14 GeV/${\mathit{c}}^2$. This is the first reported limit for charge $\frac{1}{3}e$ Long-lived fractionally charged leptons are definitely ruled out over a significant range of masses.