First evidence of neutrinos from the CNO fusion cycle in the Sun
Daniele Guffanti (Institute of Physics, JGU Mainz)

The Sun, as all the other stars, is fueled for most of its life by the fusion of hydrogen into helium taking place in its core. Neutrinos produced in such reactions are the only direct probe to the innermost part of our star and real time messengers of its engine. Decades of experimental and phenomenological efforts allowed us to study in detail the driving energy production mechanism in the Sun, the proton-proton chain, which is responsible for ~99% of the Sun luminosity. The fusion processes accounting for the remaining 1% are believed to be catalyzed by the presence of Carbon, Nitrogen and Oxygen (CNO-cycle) in the Sun interior, but a direct evidence of the occurrence of such mechanism was still missing.

After years-long efforts, the Borexino experiment at the Gran Sasso National Laboratories has recently reported the first direct observation of solar neutrinos produced in the CNO-cycle. In this talk I will present the Borexino findings and I will discuss the importance of CNO neutrinos for astrophysics and for our understanding of the Sun, particularly in connection to its chemical composition.