Experimental limits on magnetic monopole catalysis of nucleon decay

A search for superheavy magnetic monopoles ''catalyzing'' nucleon decay via the reaction M+N..-->..M+e/sup +/+mesons in an underground water Cherenkov detector has been carried out. No positive evidence for such a process has been found during 100 d of detector live time. Within the cross section and velocity ranges sigma/sub c/> or =0.1 mb and 10/sup -6/< or =..beta../sub m/< or =10/sup -1/ sigma/sub c/- and ..beta../sub m/-dependent limits on the monopole flux are presented which go as low as F/sub m/<7.2 x 10/sup -15/ cm/sup -2/ sr/sup -1/ s/sup -1/ (90% C.L.). For very low cross sections, velocity-independent limits on the monopole flux and interaction rate are obtained.