Collaborative Research: Solar Neutrino Science with Borexino

Princeton University, Princeton NJ

Investigators

Abstract

Solar neutrino research has already discovered massive neutrinos and flavor mixing and is moving into an era where precision measurements can provide a unique probe of the structure and composition of the Sun. The carbon-nitrogen-oxygen (CNO) cycle is one of the fusion reactions by which stars convert hydrogen to helium, releasing electron-neutrinos. The CNO neutrino flux depends on the abundance of carbon in the core of the Sun. A measurement of the CNO flux would be the first direct measurement of the solar metallicity (the abundance of elements other than hydrogen or helium) in the core of the Sun. It could test the fundamental assumption of homogeneity in the Sun and provide crucial information regarding opacities in the solar interior that are important for helioseismology. Such studies could thus have a great impact on our understanding of the Sun, stellar astrophysics, the link between planetary and stellar formation, as well as basic neutrino physics. Borexino is a liquid scintillator detector, located at the Gran Sasso National Laboratory in Italy, with a unique sensitivity to solar neutrinos. The Borexino research program has involved many undergraduate and graduate students. Mentoring and training young researchers at the collaborating institutions and other schools has always been a high priority. The three groups will continue to involve undergraduate students in this research and disseminate research to the broader community. The research funded here plans to measure neutrinos from the catalytic reactions on 12-C and 15-N which convert four protons to 4-He, producing neutrinos from the beta decays of 13-N and 15-O. The CN neutrino flux depends directly on the abundance of 12-C and 15-N in the core of the Sun, and their measurement would be the first direct measurement of the metallicity (elements heavier than 4-He), in the core of the Sun. This result will be far reaching because the solar composition is the basis for many important topics in astrophysics, including stellar structure, stellar evolution, and stellar atmospheres, to name a few. In addition, it will address the 'solar composition problem', the apparent disagreement in metallicity determined from recent advances in analysis of solar photospheric optical spectra, which favors a low metallicity, and advances in helioseismology, which favors high metallicity. Since modifications of the Standard Solar Model to explain a non-uniform solar composition have not been very successful, the 'solar composition problem' remains an unexplained flaw in the Standard Solar Model. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.