Search for Proton Decay into<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi>e</mml:mi></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:mrow><mml:mrow><mml:msup><mml:mrow><mml:mi>π</mml:mi></mml:mrow><mml:mrow><mml:mn>0</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>

Observations were made 1570 meters of water equivalent underground with an 8000-metric-ton water Cherenkov detector. During a live time of 80 d no events consistent with the decay $p\ensuremath{\rightarrow}{e}^{+}{\ensuremath{\pi}}^{0}$ were found in a fiducial mass of 3300 metric tons. It is concluded that the limit on the lifetime for bound plus free protons divided by the ${e}^{+}{\ensuremath{\pi}}^{0}$ branching ratio is $\frac{\ensuremath{\tau}}{B}&gt;6.5\ifmmode\times\else\texttimes\fi{}{10}^{31}$ yr; for free protons the limit is $\frac{\ensuremath{\tau}}{B}&gt;1.9\ifmmode\times\else\texttimes\fi{}{10}^{31}$ yr (90% confidence). Observed cosmic-ray muons and neutrinos are compatible with expectations.