ABSTRACT
Solar neutrinos are one of the longest standing and most interesting problems in particle astrophysics. From the astrophysical point of view, solar neutrinos are the only objects besides the study of solar oscillations (helioseismology) which allow us a direct view into the solar interior. The study of the fusion processes in the Sun via neutrino spectroscopy offers a unique perspective. From the particle physics point of view, the baseline Sun-Earth with an average of 1.496 × 108 km and neutrino energies of about 1 MeV allows probing of neutrino oscillation parameters of Δm2 ≈ 10−10 eV2, which is not possible by terrestrial means. The Sun is a pure source of νe resulting from fusion chains. During recent decades it has been established that significantly fewer solar νes are observed than would be expected from theoretical modelling. It is extremely important to find out to what extent this discrepancy points to “new physics” like neutrino oscillations, rather than to an astrophysical problem such as a lack of knowledge of the structure of the Sun or of reactions in its interior or a “terrestrial” problem of limited knowledge of capture cross sections in neutrino detectors. Nowadays the amount of data confirmed the neutrino oscillation hypothesis, and this is the third piece of evidence for a nonvanishing neutrino mass. In the following chapter the situation is discussed in more detail.
