Search for Quarks and Heavy Stable Particles Produced at 300 GeV

We report a search for quasistable particles with anomalous charge or large mass produced by the interaction of 300-GeV protons at the National Accelerator Laboratory. Analyses of energy losses in a counter telescope lead to cross-section limits of ${10}^{-35\mathrm{}}$ ${\mathrm{cm}}^2$ for particles with charges of $\frac{e}{3}$ and $\frac{2e}{3}$ and 5×${10}^{-31\mathrm{}}$ ${\mathrm{cm}}^2$ for charge-$\frac{4e}{3}$ particles. Time-of-flight measurements gave cross-section limits of about ${10}^{-31\mathrm{}}$ ${\mathrm{cm}}^2$ for the production of massive charged particles.