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 beside the study of solar oscillations (helioseismology) which allow us a direct view into the solar interior. The study of the fusion processes going on in the Sun 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 offers a chance to probe neutrino oscillation parameters of m2 ≈ 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 especially those from the Sudbury Neutrino Observatory experiment indeed strongly favour the neutrino oscillation hypothesis, and this is the third piece of evidence for a non-vanishing neutrino mass. In the following chapter the situation is discussed in more detail.