We report an upper limit on the flux of relativistic monopoles based on the nonobservation of in-ice showers by the Radio Ice Cherenkov Experiment (RICE) at the South Pole. We obtain a 95% C.L. limit of order ${10}^{-18}({\mathrm{cm}}^2\mathrm{s}\mathrm{sr}{)}^{-1}$ for intermediate-mass monopoles of ${10}^7\le \gamma \le {10}^{12}$ at the anticipated energy $E_{\mathrm{tot}}={10}^{16}\mathrm{GeV}$. This bound is over an order of magnitude stronger than all previously published experimental limits for this range of boost parameters $\gamma$ and exceeds 2 orders of magnitude improvement over most of the range. We review the physics of radio detection, describe a Monte Carlo simulation including continuous and stochastic energy losses, and compare to previous experimental limits.

• Received 12 June 2008

DOI:https://doi.org/10.1103/PhysRevD.78.075031