Experimental Limits on Magnetic Monopole Catalysis of Nucleon Decay

A search for superheavy magnetic monopoles "catalyzing" nucleon decay via the reaction $M+N\ensuremath{\rightarrow}M+{e}^{+}+\mathrm{mesons}$ in an undergound water Cherenkov detector has been carried out. No positive evidence for such a process has been found during 100 d of detector live time. Cross section and velocity-dependent limits on the monopole flux are presented which are as low as ${F}_{m}<7.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$ ${\mathrm{cm}}^{\ensuremath{-}2}$ ${\mathrm{sr}}^{\ensuremath{-}1}$ ${\mathrm{s}}^{\ensuremath{-}1}$ (90% C.L.). For very low cross sections, velocity-independent limits on the monopole flux and interaction rate are obtained.