A Search for Proton Decay into e+π° Irvine-Michigan-Brookhaven Collaboration

Observations were made 1570 mwe underground with an 8000 metric ton water Cherenkov detector. During a live-time of 80 days no events consistent with the decay p → e+π° were found in a fiducial mass of 3300 metric tons. We conclude that the limit on the lifetime for bound plus free protons divided by the e+π° branching ratio is τ/B > 1.9 × 1031 yr. (90% confidence). Observed cosmic ray muons and neutrinos are compatible with expectations.