Upper limits to the diffuse neutrino emission from active galactic nuclei

In November of 1987 a muon detector dubbed the Short Prototype String (SPS) was successfully operated for about 30 hours in the deep ocean approximately 35 km west of the big island of Hawaii. The original purpose of the experiment was to demonstrate the technical feasibility of conducting neutrino astronomy in the deep ocean, and to serve as the prototype to the DUMAND experiment. Hence, the data were originally analyzed to measure the deep ocean flux of atmospheric muons as a proof of concept. The more recent theoretical investigations of neutrino production in Active Galactic Nuclei (AGN) has motivated a search of the data for the unique signature of neutrino-induced particle cascades. The optical properties of the deep ocean allows for surprisingly large detection volumes that grow with incident neutrino energy. It is found through Monte Carlo simulation that the fiducial mass for this type of search is {dollar}sim{dollar}7 {dollar}times{dollar} 10{dollar}sp6{dollar} tons of water at incident neutrino energies of 1 PeV (10{dollar}sp{lcub}15{rcub}{dollar}eV). This results in an exposure of 19.2 kton-years (kty) at this energy for 24 hours of operation. No evidence for neutrino-induced cascades was found in {dollar}sim{dollar}20 hours of detector livetime. This leads to the most stringent limits of AGN neutrino fluxes above the PeV scale yet published.