Search for proton decay into positron plus neutral pion and positive muon plus neutral pion

132 days of data corresponding to 4 x 1032 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 1030 to 1032 years as predicted in the recent grand unification theories. 18.5 million event triggers were scanned for the decay modes: p → e+π0, and μ+π0. No events are observed for the e+π0 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+π0) greater than or equal to 8.1 x 1031 years. In addition a lifetime independent of nuclear effects for the e+π0 mode can be obtained and is: tau/B (free p → e+π0) greater than or equal to 2.4 x 1031 years. Two candidates consistent with the expected neutrino background are observed as potential μ+π0 bound proton decay and no candidates are seen satisfying the requirements for decay from free protons. The calculated lifetimes are: tau/B (all p → μ+π0) greater than or equal to 3.4 x 1031 years and tau/B (free p → μ+π0) greater than or equal to 2.3 x 1031 years