A STUDY ON THE E MU IDENTIFICATION CAPABILITY OF A WATER CERENKOV DETECTOR AND THE ATMOSPHERIC NEUTRINO PROBLEM/

We carried out an experimental test of various characteristics of a wa ter Cerenkov detector, especially the particle identification capabili ty, using the 12-GeV proton synchrotron at KEK, Japan. The detector ch aracteristics so far studied are well reproduced by the Monte Carlo si mulation. Especially it is able to identify electrons and muons with m is-identification probabilities less than a few percent in the momentu m range of 250-1000 MeV/c except the particle positions in the extreme edge of the detector volume. Based on the present results, the defici ency of mu-neutrinos in the atmospheric neutrinos is not an artifact c aused by some peculiar detector characteristics.