Experimental study of the atmospheric neutrino backgrounds for p -> e(+)pi(0) searches in water Cherenkov detectors

The atmospheric neutrinobackground for proton decayvia p→e + π 0 in ring imaging water Cherenkov detectorsis studied with an artificial accelerator neutrinobeam for the first time. In total, 3.14 × 10 5 neutrinoevents corresponding to about 10 megaton-years of atmospheric neutrinointeractions were collected by a 1000 ton water Cherenkov detector(KT). The KT charged-currentsingle π 0 production data are well reproduced by simulation programs of neutrinoand secondary hadronic interactions used in the Super-Kamiokande(SK) proton decaysearch. The obtained p→ e + π 0 background rate by the KT data for SK from the atmospheric neutrinoswhose energies are below 3 GeV is 1.63 +0.42 -0.33 (stat) +0.45 -0.51 (syst)(megaton-year) -1 . This result is also relevant to possible future, megaton-scale water Cherenkov detectors.