High Energy Neutrino Astrophysics

The observation of neutrinos is an experimental challenge due to their weak interactions that makes them elusive particles. Though they are difficult to detect, they are excellent probes to observe the most distant sources and their interior. Until now only MeV extra-terrestrial neutrinos have been observed from the Sun and SN1987A. Nevertheless there is growing activity to build detectors for high energy (& 1 TeV) neutrinos of astrophysical origin: their detection would allow the observation of the horizon not accessible to the well-established γ-astronomy. In Sec. 2 the scientific objectives of ν astrophysics and the connection to the observation of Ultra-High Energy Cosmic Rays (UHECRs) are introduced. The complementarity between γ and ν-astrophysics is pointed out and typical models for ν production are considered. The working principle of Neutrino Telescopes (NTs) exploiting the Cherenkov light detection in the South Pole ice or in sea/lake depths is summarized in Sec. 3. Detector performances, event topologies and background rejection methods are considered. In Sec. 4 the current status of Cherenkov NTs is reviewed, while in Sec. 5 other techniques are considered.