Both the NOvA (NuMI Off-Axis νe Emergence Experiment) and T2K experiments involve launching neutrinos from a particle accelerator and detecting them after they traverse extensive underground distances. The challenges are significant: out of trillions of particles, only a few leave a trace that can be detected. Advanced detectors and software are then employed to reconstruct these rare events, offering insights into how the “flavor” of neutrinos alters as they travel.
The world’s first neutrino observation inside a hydrogen bubble chamber, captured on November 13, 1970, in a 12-foot bubble chamber at a zero-gradient synchrotron. Here, an invisible neutrino collides with a proton, resulting in three particle tracks (bottom right). The neutrino changes into a muon, marked by a lengthy orbit extending up and to the left. The shorter track represents the proton, while the third track extending down and to the left is the pion formed by the collision. Image credit: Argonne National Laboratory.
Neutrinos are among the most prevalent particles in the universe.
With no charge and minimal mass, they are notoriously difficult to detect. Yet, this very elusiveness contributes to their scientific significance.
Understanding neutrinos may shed light on one of the greatest mysteries in cosmology: the reason the universe consists of matter.
Theoretically, the Big Bang should have resulted in equal parts matter and antimatter, which would have completely annihilated each other upon meeting, releasing energy in the process.
However, during the Big Bang, an imbalance occurred, producing a greater abundance of matter, which eventually led to the formation of stars, galaxies, and life as we know it.
Physicists theorize that neutrinos hold the key to this conundrum.
There are three types, or “flavors,” of neutrinos: electron, muon, and tau, which are different versions of the same fundamental particle.
They possess a unique ability to oscillate, changing from one flavor to another as they traverse space. Studying these oscillations and examining any differences between neutrinos and their antimatter counterparts could provide insights into why matter triumphed over antimatter in the nascent universe.
“Understanding these various identities could help scientists gain insight into neutrino masses and address significant questions regarding the universe’s evolution, including why matter became dominant over antimatter,” stated Dr. Zoya Valari, a physicist at Ohio State University.
“What makes neutrinos particularly intriguing is their ability to change their ‘taste.’”
“Consider this: you buy chocolate ice cream, stroll down the street, and suddenly it turns mint, only to change again with every step you take.”
To delve deeper into this shape-shifting behavior, the NOvA and T2K experiments partnered to direct neutrino particle beams over hundreds of kilometers.
NOvA projects a beam of neutrinos from a source at Fermi National Accelerator Laboratory near Chicago, traveling 500 miles to a 14,000-ton detector in Ash River, Minnesota.
On the other hand, Japan’s T2K sends a neutrino beam 295 km from the J-PARC accelerator in Tokai to the enormous Super-Kamiokande detector situated beneath Mt. Ikenoyama.
“While our objectives are aligned, the distinct experimental designs mean that synthesizing the data yields more comprehensive insights, making the whole greater than the sum of its parts,” Dr. Valari remarked.
This study builds upon earlier findings that noted minor yet significant variations in the masses of different types of neutrinos. Researchers sought deeper clues indicating that neutrinos might operate beyond the conventional laws of physics.
One such inquiry involves whether neutrinos and their antimatter counterparts exhibit different behaviors—a phenomenon referred to as charge parity violation.
“Our results indicate that additional data are needed to adequately address these fundamental questions,” Dr. Valari said.
“This underscores the importance of developing the next generation of experiments.”
Research indicates that employing two experiments with varying baselines and energies is more likely to yield answers than relying solely on a single experiment. Consequently, consolidating results from both experiments allowed scientists to explore these urgent physics questions from diverse perspectives.
“This research is extremely complex, involving hundreds of contributors in each collaborative effort,” said John Beacom, a professor at Ohio State University.
“Collaboration in science is typically competitive, but our work together here highlights the high stakes involved.”
For further details, see the new discovery published in the journal Nature.
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NOvA collaboration and T2K collaboration. 2025. Joint neutrino oscillation analysis using T2K and NOvA experiments. Nature 646, 818-824; doi: 10.1038/s41586-025-09599-3
Source: www.sci.news
