Study: Neutrinos, the Ghost Particles That Could Rewrite the Physics of the Universe

A new international study sheds light on some of the most mysterious particles in the cosmos - neutrinos, the "ghosts” of matter that pass unnoticed through everything they encounter. Trillions of them pass through our bodies every second without leaving a trace, and scientists are still trying to decipher their nature. The research, published in the journal Nature, combines the results of two of the world's largest neutrino experiments, conducted in Japan and the United States, and provides unprecedented data on the structure and mass of these particles. Neutrinos are the most abundant particles in the Universe, but also among the most enigmatic. They have no electric charge, are incredibly light - almost massless - and interact extremely rarely with matter. They are produced in places of immense cosmic intensity: in the core of the Sun, in supernova explosions, or in nuclear processes inside stars. A key property of neutrinos is their ability to change from one type to another as they travel-a phenomenon known as "neutrino oscillation.” This behavior sets them apart from other elementary particles, such as electrons or protons, and hides clues about the differences in the masses of the three types-poetically called "flavors”-of neutrinos.

• Two experiments, one step forward

The two projects that contributed to the new study-T2K (Japan) and NOvA (USA)-have been tracking the oscillations of these particles over enormous distances. The NOvA experiment sends a beam of neutrinos from the Fermi National Laboratory near Chicago to a detector more than 500 miles away in Minnesota.

The T2K experiment sends neutrinos through the Earth's crust over a distance of 295 kilometers, from the Japanese city of Tokai to the Kamioka detector. Although they use different technologies and energies, both have the same goal: to precisely measure how neutrinos change during their journey. By combining data obtained over a decade, the researchers were able to determine the mass differences between two of the three types of neutrinos with unprecedented accuracy - an uncertainty of less than 2%. "At first glance, there were questions about the compatibility of the T2K and NOvA results. We found that they are, in fact, extremely compatible,” explained physicist Kendall Mahn of Michigan State University.

• Key to the Big Questions of the Cosmos

Why are these findings so important? Because neutrinos could hold the answers to some of the deepest mysteries in physics: why there is matter in the Universe, what happened to antimatter, and the nature of dark matter and energy. "This research brings us closer to understanding why the Universe is made of matter and did not completely annihilate itself at the time of the Big Bang,” said Zoya Vallari, a physicist at Ohio State University and a member of the NOvA team. If neutrinos and their counterparts, antineutrinos, behave differently, this asymmetry could explain why matter "won” the cosmic battle against antimatter.

• A new era of particle physics

The T2K and NOvA results mark a crucial step toward a new generation of giant experiments under construction: DUNE (Deep Underground Neutrino Experiment), a project coordinated by Fermilab in the US, which will connect laboratories in Illinois and South Dakota; Hyper-Kamiokande, in Gifu Prefecture, Japan, the successor to the legendary Super-Kamiokande detector; JUNO, in China, designed to study the mass structure of neutrinos with unprecedented precision.

In parallel, underwater or subglacial telescopes such as KM3NeT and IceCube are searching for neutrinos from deep space, to observe the most violent phenomena in the Universe. "Neutrinos have unique properties, and we are still learning a lot about them,” concluded Kendall Mahn.