The Highest Energy Neutrinos

TL;DR

This paper discusses the potential of kilometer-scale neutrino detectors to identify cosmic ray sources by detecting high-energy neutrinos, highlighting technological advances and the need for even larger detectors for extragalactic sources.

Contribution

It provides a model-independent analysis of the feasibility of large neutrino detectors and emphasizes recent technological breakthroughs enabling their construction.

Findings

Kilometer-scale detectors are feasible and promising for detecting cosmic neutrinos.

Technological hurdles for large detectors have been overcome.

Even larger detectors are needed to probe extragalactic sources via GZK neutrinos.

Abstract

Measurements of the arrival directions of cosmic rays have not revealed their sources. High energy neutrino telescopes attempt to resolve the problem by detecting neutrinos whose directions are not scrambled by magnetic fields. The key issue is whether the neutrino flux produced in cosmic ray accelerators is detectable. It is believed that the answer is affirmative, both for the galactic and extragalactic sources, provided the detector has kilometer-scale dimensions. We revisit the case for kilometer-scale neutrino detectors in a model-independent way by focussing on the energetics of the sources. The real breakthrough though has not been on the theory but on the technology front: the considerable technical hurdles to build such detectors have been overcome. Where extragalactic cosmic rays are concerned an alternative method to probe the accelerators consists in studying the arrival directions of neutrinos produced in interactions with the microwave background near the source, i.e. within a GZK radius. Their flux is calculable within large ambiguities but, in any case, low. It is therefore likely that detectors that are larger yet by several orders of magnitudes are required. These exploit novel techniques, such as detecting the secondary radiation at radio wavelengths emitted by neutrino induced showers.