Search for Proton Decay via p -> e+ pi0 in a Large Water Cherenkov   Detector
  We have searched for proton decay via p -> e+ pi0 using data from a 25.5 kton-year exposure of the Super-Kamiokande detector. We find no candidate events with an expected background induced by atmospheric neutrinos of 0.1 events. From these data, we set a lower limit on the partial lifetime of the proton to be 1.6E33 years at a 90% confidence level. 
The Super-Kamiokande Collaboration: M. Shiozawa, et al