It is 70 years since the discovery of the neutrino: the breakthrough that changed physics

On 20 July, 70 years ago, a discovery that changed the history of physics was published in the journal *Science*: two American researchers, Frederick Reines and Clyde Cowan, had succeeded in detecting antineutrinos for the first time, thereby also confirming the existence of the elusive neutrinos. Throughout the 20th century, neutrino physics has taken on an increasingly central role in fundamental research, but several questions remain unanswered.

“As far as the neutrino is concerned, there are still many unsolved mysteries,” Marco Pallavicini, a physicist at the National Institute of Nuclear Physics and a professor at the University of Genoa, told ANSA. “For example, we still do not know whether it is a particle distinct from its antiparticle, or whether the neutrino and the antineutrino are one and the same. Furthermore, we still do not know the value of its mass, despite many experiments having attempted to measure it. Another mystery,” continues Pallavicini, “concerns the emission of the ultra-high-energy neutrinos that have been detected; their astrophysical origin remains unknown.”

Neutrinos are also known as ‘ghost particles’ because they interact so little with matter that they can travel across the universe without colliding with almost anything. This ability makes them extremely difficult to detect, but it also enables them to carry valuable information about environments that would otherwise be impossible to explore. “Whether for the study of the fundamental forces of nature or for astrophysics,” says Pallavicini, “neutrinos are unique detection tools and carriers of information.”

The experiment set up by Reines and Cowan in 1956 to detect this particle was part of a project called Poltergeist, a German word (‘ghost’) chosen precisely to evoke the elusiveness of the neutrino. It consisted of a series of detectors containing tanks of water and scintillating liquids – substances that emit light when charged particles pass through them. This light serves as the tell-tale sign of the interaction of the antineutrino produced in the reactor.

“These were new technologies for the time,” comments the physicist from the INFN, “which only became standard many years later.” Now, 70 years on, new and increasingly complex experiments are under construction with the aim of writing new chapters in the history of physics. Among these are the CUPID and LEGEND experiments, based at the INFN’s Gran Sasso National Laboratories: both are dedicated to determining whether or not neutrinos correspond to their antiparticles.