a Search for Proton Decay Into Positron Plus Neutral Pion and Positive Muon Plus Neutral Pion.

132 days of data corresponding to 4 x 10('32) proton years of exposure has been analyzed in the Irvine -Michigan-Brookhaven water Cerenkov nucleon decay detector. The analysis has concentrated on multi-track contained events in which the tracks are thought to be the likely products of proton decay with lifetimes of 10('30) to 10('32) years as predicted in the recent grand unification theories. 18.5 million event triggers were scanned for the decay modes: p (--->) e('+)(pi)('0), and (mu)('+)(pi)('0). No events are observed for the e('+)(pi)('0) mode from either free or bound protons. Based on this, a new lower limit on the lifetime of the proton for this postulated mode divided by the branching ratio at the 90% confidence level is: (tau)/B (all p (--->) e('+)(pi)('0)) (GREATERTHEQ) 8.1 x 10('31) years. In addition a lifetime independent of nuclear effects for the e('+)(pi)('0) mode can be obtained and is: (tau)/B (free p (--->) e('+)(pi)('0)) (GREATERTHEQ) 2.4 x 10('31) years. Two candidates consistent with the expected neutrino background are observed as potential (mu)('+)(pi)('0) bound proton decay and no candidates are seen satisfying the requirements for decay from free protons. The calculated lifetimes are: (tau)/B (all p (--->) (mu)('+)(pi)('0)) (GREATERTHEQ) 3.4 x 10('31) years and (tau)/B (free p ( --->) (mu)('+)(pi)('0)) (GREATERTHEQ) 2.3 x 10('31) years.