Abstract
We outline the current situation in ultrahigh energy (UHE) cosmic ray physics, pointing out the remaining problems, in particular the puzzle concerning the origin of the primary radiation and the role of neutrino astronomy for locating the sources. Various methods for the detection of UHE neutrinos are briefly described and their merits compared. We give an account of the achievements of the existing optical Cherenkov neutrino telescopes, outline the possibility of using air fluorescence and particle properties of air showers to identify neutrino induced events, and discuss various pioneering experiments employing radio and acoustic detection of extremely energetic neutrinos. The next generation of space, ground and sea based neutrino telescopes now under construction or in the planning phase are listed.
Highlights
The principal aim of neutrino astronomy is to locate the sources of ultrahigh energy (UHE) component of the cosmic radiation (CR)
It is expected that UHE hadronic interactions take place within the sources and in their immediate vicinity, copiously producing pions, kaons and other particles that are subject to decay, yielding a corresponding number of photons and neutrinos of different flavors
After re-scaling the energy spectra of all major experiments of recent years, there is good agreement with respect to the shape of the spectrum, i.e., the spectral index, and the intensity to within about 20 percent or better up to ∼ 5 × 1019 eV. Beyond this energy even the two most recent and largest experiments, the Telescope Array (TA) [48] in the northern hemisphere and the Pierre Auger Observatory (PAO) [5] in the southern hemisphere, show increasing differences between their respective spectra with increasing energy as they enter the region of the expected Greisen–Zatsepin–Kuzmin (GZK) cutoff [32, 59]
Summary
The principal aim of neutrino astronomy is to locate the sources of UHE component of the cosmic radiation (CR). After re-scaling the energy spectra of all major experiments of recent years, there is good agreement with respect to the shape of the spectrum, i.e., the spectral index, and the intensity to within about 20 percent or better up to ∼ 5 × 1019 eV Beyond this energy even the two most recent and largest experiments, the Telescope Array (TA) [48] in the northern hemisphere and the Pierre Auger Observatory (PAO) [5] in the southern hemisphere, show increasing differences between their respective spectra with increasing energy as they enter the region of the expected Greisen–Zatsepin–Kuzmin (GZK) cutoff [32, 59] (see Fig. 1a). Νμ, μ+ → e+ + νμ + νe, and n → p + e− + νe, and similar reactions, which cause the cutoff
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