Detection of Atmospheric Neutrinos in the HPW Experiment.

A search was undertaken to study upward going neutrinos of atmospheric origin that penetrated the earth and reached the HPW large underground water Cerenkov detector. This is a 702 metric ton detector instrumented with a volume array of 704 photomultiplier tubes that was originally built by the Harvard-Purdue-Wisconsin collaboration for the study of nucleon decay. Data were analysed for a period of 0.1397 years. Three candidate events were found for neutrinos interacting inside the volume of the detector corresponding to a total rate of 168 +/- 56 atmospheric neutrinos/kT/yr with energies above 300 MeV. Seven candidate events were found for penetrating upward going nu_mu-induced muons corresponding to a flux of (3.37 +/- 0.48) times 10^ {13} muons/sec/cm^2/sr with energies above 300 MeV.