Search for Ultra High-Energy Neutrinos with AMANDA-II

TL;DR

This paper reports a search for ultra high-energy neutrinos using AMANDA-II data from 2000-2002, setting upper limits on neutrino fluxes and constraining models of neutrino sources like active galactic nuclei.

Contribution

First search for diffuse ultra high-energy neutrinos with AMANDA-II, establishing flux limits and excluding certain astrophysical models.

Findings

No significant excess of neutrinos detected.

Set upper limits on neutrino fluxes in the 2x10^5 to 10^9 GeV range.

Excluded some active galactic nuclei neutrino flux models.

Abstract

A search for diffuse neutrinos with energies in excess of 10^5 GeV is conducted with AMANDA-II data recorded between 2000 and 2002. Above 10^7 GeV, the Earth is essentially opaque to neutrinos. This fact, combined with the limited overburden of the AMANDA-II detector (roughly 1.5 km), concentrates these ultra high-energy neutrinos at the horizon. The primary background for this analysis is bundles of downgoing, high-energy muons from the interaction of cosmic rays in the atmosphere. No statistically significant excess above the expected background is seen in the data, and an upper limit is set on the diffuse all-flavor neutrino flux of E^{-2} $\Phi$_{90%CL} < 2.7 $\times$ 10^{-7} GeV cm^{-2} s^{-1} sr^{-1} valid over the energy range of 2 $\times$ 10^5 GeV to 10^9 GeV. A number of models which predict neutrino fluxes from active galactic nuclei are excluded at the 90% confidence level.