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

The atmospheric neutrino background for proton decay via p → e⁺π⁰ in ring imaging water Cherenkov detectors is studied with an artificial accelerator neutrino beam for the first time. In total, 3.14×10⁵ neutrino events corresponding to about 10 megaton-years of atmospheric neutrino interactions were collected by a 1,000 ton water Cherenkov detector (KT). The KT charged-current single p0 production data are well reproduced by simulation programs of neutrino and secondary hadronic interactions used in the Super–Kamiokande (SK) proton decay search. The obtained p → e⁺π⁰ background rate by the KT data for SK from the atmospheric neutrinos whose 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.