NEUTRINOS

In this case too, the first theoretical hypothesis about the existence of neutrino oscillation (formulated by Bruno Pontecorvo in 1957) had to wait many years before it was experimentally verified. This occurred first for atmospheric neutrinos in 1998 (thanks to the Japanese Super-Kamiokande experiment) and, subsequently, for neutrinos produced in the laboratory, over the course of several experiments. One of these is OPERA, which measured the oscillation of neutrinos produced at CERN and sent to the INFN Gran Sasso National Laboratory. The experiments for detecting neutrinos exploit large tanks of liquid substances, like heavy water or gallium chloride, in many cases. Detection occurs through rare, but measurable, interactions of neutrinos with atoms in the liquid. Other experiments take place in enormous underground facilities to reduce interference from other radiation sources.

Neutrinos may be produced in various physical processes, like nuclear decay and astrophysical phenomena. They are some of the most abundant particles in the universe: every second, billions of neutrinos coming from the Sun traverse our body, without causing any appreciable effects.
Their ability to traverse matter almost entirely undisturbed constitutes, on the one hand, a big obstacle to the possibility of observing them. On the other hand, it makes them carriers of very precious information about astrophysical events, like the formation of stars, supernovae explosions, and the composition of the primordial universe. It is no coincidence that the most recent experimental efforts are directed at researching astrophysical and cosmological neutrinos, as well as, of course, studying neutrinos of the Sun. The latter is the closest and most abundant source. In this area, INFN has played a fundamental role with the Borexino experiment, operating from 2007 to 2021 at the Gran Sasso Laboratories, which has obtained very significant results for understanding the physics of solar neutrinos.