The new frontier in this field is the study of the low energy part of the solar neutrino spectrum, which represents the great majority of the spectrum and is still an almost unexplored realm.
The solar neutrino experiments presently running or planned for the future can contribute to solve at least some of these puzzles. At the same time, the possibility of measuring directly at least some components of the solar neutrino spectrum and of recovering in an indirect way the value of total solar neutrino flux have been fundamental for the progressive refinement of the standard solar model (SSM), which evolved during these years and is now in a general good agreement with the solar neutrino experiments.ĭespite the fundamental steps forward made in the last decades, many questions are still open about the real nature and the main properties of neutrinos and the exact mixing mechanism, for example, are neutrinos Majorana or Dirac fermions, the determination of mass hierarchy and exact mass values, accurate determination of the mixing angles, and presence of CP violation. Therefore, it is clear why these results had a great impact on elementary particle physics and also on cosmological models. This is one of the first pieces of clear evidence of the need to go beyond the standard model of electroweak interactions and the attempt to accommodate the experimental results about neutrino masses and mixing is a test that every theory “beyond the Standard Model” has to pass. The experimental results obtained using different techniques in more than thirty years and the parallel theoretical advancements confirmed at the end the validity of Pontecorvo’s revolutionary idea of neutrino oscillation, proving in a crystal clear way that neutrinos are massive and oscillating particles. But the surprising result of an apparent deficit in the electron neutrino flux reaching the detector marked the raise of the so-called solar neutrino puzzle and opened a whole new field of research, that has been central in elementary particle physics for many decades. The pioneering work in the sixties had the main goal of understanding better the way in which our star shines and to test solar models. The analysis of neutrinos emitted in the fusion processes inside the Sun is one of most significant examples of the relevant role played by the study of neutrino properties in elementary particle physics and astrophysics and in creating a link between these two sectors. We discuss this research project and the way in which present and future experiments could contribute to make the theoretical framework more complete and stable, understanding the origin of some “anomalies” that seem to emerge from the data and contributing to answer some present questions, like the exact mechanism of the vacuum to matter transition and the solution of the so-called solar metallicity problem. The main focus at the moment is to improve the knowledge of the mass and mixing pattern and especially to study in detail the lowest energy part of the spectrum, which represents most of the solar neutrino spectrum but is still a partially unexplored realm. After reviewing the striking results of the last two decades, which were determinant to solve the long standing solar neutrino puzzle and refine the Standard Solar Model, we focus our attention on the more recent results in this field and on the experiments presently running or planned for the near future. Relevant indications on the fundamental interactions among particles.
The study of solar neutrinos has given a fundamental contribution both to astroparticle and to elementary particle physics, offering an ideal test of solar models and offering at the same time