On July 20, 70 years ago, the 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 , thus also confirming the existence of the elusive neutrinos .
Over the course of the 20th century, neutrino physics has assumed an increasingly central role in fundamental research, but several questions still remain unanswered.
“As for the neutrino, there are still many unsolved mysteries ,” Marco Pallavicini, a physicist at the National Institute for Nuclear Physics and professor at the University of Genoa, told ANSA. “For example, we still don’t know whether it is a different particle from its antiparticle , or whether neutrinos and antineutrinos coincide. Furthermore, we still don’t know the value of its mass , despite many experiments having attempted to measure it. Another mystery,” Pallavicini continues, “concerns the emission of very high-energy neutrinos that have been detected; their astrophysical origin remains unknown .”
Neutrinos are also called ‘ ghost particles ‘ because they interact so little with matter that they can travel through the universe without colliding with almost anything. This ability makes them extremely difficult to intercept and allows them to carry precious information about environments that would otherwise be impossible to explore . “Both for the study of the forces of nature and for astrophysics ,” Pallavicini states, “neutrinos are unique means of detection and carriers of information .”
The experiment set up by Reines and Cowan in 1956 to intercept this particle was part of a project called Poltergeist , a German word (‘ghost spirit’) 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 represents the telltale signal of the interaction of the antineutrino produced in the reactor. ” These were new technologies for the time ,” comments the INFN physicist, “which only became standard many years later.”
Now, 70 years later, increasingly complex experiments are being designed with the aim of writing new pages in the history of physics. Among these are the Cupid and Legend experiments located at the INFN’s Gran Sasso National Laboratories: both are dedicated to understanding whether neutrinos correspond to their antiparticles.
” These two experiments will write the future of researchof the next 10-15 years ,” says Pallavicini. Then there is the underwater neutrino telescope KM3NeT , also from the INFN: a structure built at a depth of 2,000 meters off the coast of Sicily designed to observe neutrinos coming from the most remote places in the cosmos, which should reach its final configuration by 2030. Finally, outside Italy, other large experiments are coming to life, such as Hyper-Kamiokande , the gigantic neutrino observatory under construction in Japan, and Juno in China. “These experiments,” concludes Pallavicini, “will drastically improve our knowledge of neutrinos.”
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