We report the first result of a search for highly ionizing particles in $e^{+}$$e^{\mathrm{-}}$ annihilations at the KEK storage ring TRISTAN. CR-39 and UG-5 dielectric track detectors were exposed to 4.8 ${\mathrm{pb}}^{\mathrm{-}1}$ integrated luminosity at total energies of 50–52 GeV in the center of mass. This search is sensitive to Dirac magnetic monopoles and yields 95% confidence-level upper limits of 8×${10}^{\mathrm{-}37}$ and 1.3×${10}^{\mathrm{-}35}$ ${\mathrm{cm}}^2$ on the cross section for production of monopoles with magnetic charges g=68.5e≡$g_D$ and g=2$g_D$ and respective maximum masses 24.1 and 22.0 GeV/$c^2$.

• Received 15 January 1988

DOI:https://doi.org/10.1103/PhysRevLett.60.1610