Search for Supermassive Magnetic Monopoles Using Mica Crystals

The observed absence of monopole tracks in large, ancient mica crystals enables us to set an upper limit of less than ∼ ${10}^{-18\mathrm{}}$ ${\mathrm{cm}}^{-2\mathrm{}}$ ${\mathrm{sr}}^{-1\mathrm{}}$ ${\mathrm{s}}^{-1\mathrm{}}$ on the flux of supermassive monopoles with $0.0004c<V<\mathrm{}0.0015c$ that are stably attached to nuclei. This limit takes into account the fraction of monopoles not initially bound to protons, the fraction that attach with nuclei on their way to the mica, and the measured storage times for tracks with thermal stability similar to that of monopole tracks.