Experimental Limits on Magnetic Monopole Catalysis of Nucleon Decay

A search for superheavy magnetic monopoles "catalyzing" nucleon decay via the reaction $M+N\to M+e^{+}+\mathrm{mesons}$ 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 $F_m<7.2\mathrm{}\times {10}^{-15\mathrm{}}$ ${\mathrm{cm}}^{-2\mathrm{}}$ ${\mathrm{sr}}^{-1\mathrm{}}$ ${\mathrm{s}}^{-1\mathrm{}}$ (90% C.L.). For very low cross sections, velocity-independent limits on the monopole flux and interaction rate are obtained.