Background Study on nu_e Appearance from a nu_mu Beam in Very Long Baseline Neutrino Oscillation Experiments with a Large Water Cherenkov Detector

There is a growing interest in very long baseline neutrino oscillation experimentation using accelerator produced neutrino beam as a machinery to probe the last three unmeasured neutrino oscillation parameters: the mixing angle theta_13, the possible CP violating phase delta_CP and the mass hierarchy, namely, the sign of delta-m^2_32. Water Cherenkov detectors such as IMB, Kamiokande and Super-Kamiokande have shown to be very successful at detecting neutrino interactions. Scaling up this technology may continue to provide the required performance for the next generation of experiments. This report presents the latest effort to demonstrate that a next generation (> 100 kton) water Cherenkov detector can be used effectively for the rather difficult task of detecting nu_e events from the neutrino oscillation nu_mu -> nu_e despite the large expected potential background resulting from pi^0 events produced via neutral current interactions.