A Search for High Energy Neutrinos from Active Galactic Nuclei

We report the results of a search for neutrino-induced particle cascades using a deep ocean water Čerenkov detector. Previous results using this instrument have demonstrated its effectiveness for tracking cosmic-ray muons in depths up to 4.2 km. Here we analyze the same data to search for the possible signature of ultra-high energy neutrinos. Potentially detectable fluxes of such neutrinos are predicted to come from active galactic nuclei according to some models. The effective mass of the detector, a string of seven 40 cm photomultipliers at 5.2 m spacing, is found through simulation analysis to be surprisingly large: greater than 10 tons of water at incident neutrino energies of 10 GeV . We find no evidence for neutrino-induced cascades in ∼ 20 hrs of operation. Although the limit implied by this observation is the strongest yet for predictions of active galatic nuclei (AGN) neutrinos at energies above 100 TeV, perhaps the more intriguing result is that the power of these techniques can be exploited to test these AGN models in a relatively short time. Subject headings: Active galactic nuclei: neutrinos : cosmic rays