Search for superheavy grand unified magnetic monopoles in cosmic rays

A search for superheavy grand unified magnetic monopoles has been performed utilizing a 7.3×7.3-${\mathrm{m}}^2$ array of scintillation counters, sited underground at a depth of 1148 hg/${\mathrm{cm}}^2$. This apparatus measures both the time of flight and specific ionization of particles passing through it and has a trigger which is sensitive to prompt as well as very slowly developing pulses from the detector. No monopole events were observed during 6700 h of live-time operation of this detector, yielding an upper limit on the flux of monopoles of 4.6×${10}^{\mathrm{-}14}$ ${\mathrm{cm}}^{\mathrm{-}2}$ ${\mathrm{sr}}^{\mathrm{-}1}$ ${\sec }^{\mathrm{-}1}$ (90% confidence level) in the velocity range 8.5×${10}^{\mathrm{-}4}$c to 0.012c.