Hidden clues in ghostly particles could explain why we exist
Scientists working together across continents have made one of the most precise studies ever of mysterious particles called neutrinos.
- Date:
- October 30, 2025
- Source:
- Michigan State University
- Summary:
- In a rare global collaboration, scientists from Japan and the United States joined forces to explore one of the universe’s deepest mysteries — why anything exists at all. By combining years of data from two massive neutrino experiments, researchers took a big step toward understanding how these invisible “ghost particles” might have tipped the cosmic balance in favor of matter over antimatter.
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A Michigan State University researcher has helped lead a groundbreaking effort that brings scientists closer to uncovering how the universe came to be.
For the first time, two of the world's largest neutrino experiments -- T2K in Japan and NOvA in the United States -- have combined their data to achieve unprecedented precision in studying neutrinos, the nearly invisible particles that fill the cosmos but rarely interact with anything.
Their joint analysis, recently published in Nature, offers the most accurate measurements yet of how neutrinos change from one type to another as they travel through space. This milestone paves the way for future research that could deepen our understanding of the universe's evolution -- or even challenge current scientific theories.
Kendall Mahn, a professor of physics and astronomy at Michigan State University and co-spokesperson for T2K, helped coordinate the collaboration. By uniting the strengths of both experiments, the teams achieved results that neither could have reached on its own.
"This was a big victory for our field," Mahn said. "This shows that we can do these tests, we can look into neutrinos in more detail and we can succeed in working together."
Why Matter Exists at All
According to physicists, the early universe should have contained equal amounts of matter and antimatter. If that had been the case, the two would have annihilated each other completely. Yet, matter somehow survived -- and we have no clear reason why.
Many researchers believe the answer may be hidden in the strange behavior of neutrinos, tiny particles that constantly pass through us but rarely interact. Understanding a process called neutrino oscillation, where these particles change "flavors" as they move, could help explain why matter triumphed over antimatter.
"Neutrinos are not well understood," said MSU postdoctoral associate Joseph Walsh, who worked on the project. "Their very small masses mean they don't interact very often. Hundreds of trillions of neutrinos from the sun pass through your body every second, but they will almost all pass straight through. We need to produce intense sources or use very large detectors to give them enough chance to interact for us to see them and study them."
How the Experiments Work
Both T2K and NOvA are known as long-baseline experiments. Each sends a focused beam of neutrinos toward two detectors -- one near the source and another hundreds of miles away. By comparing results from both detectors, scientists can track how neutrinos change along the way.
Because the experiments differ in design, energy, and distance, combining their data gives researchers a more complete picture.
"By making a joint analysis you can get a more precise measurement than each experiment can produce alone," said NOvA collaborator Liudmila Kolupaeva. "As a rule, experiments in high-energy physics have different designs even if they have the same science goal. Joint analyses allow us to use complementary features of these designs."
The Puzzle of Neutrino Mass
A major focus of the study is something called "neutrino mass ordering," which asks which neutrino type is the lightest. This isn't as simple as weighing particles on a scale. Neutrinos exist in three mass states, and each flavor of neutrino is actually a mixture of those states.
Scientists are trying to determine whether the mass arrangement follows a "normal" pattern (two light and one heavy) or an "inverted" one (two heavy and one light). In the normal case, muon neutrinos are more likely to become electron neutrinos, while their antimatter partners are less likely to do so. The reverse occurs in the inverted pattern.
An imbalance between neutrinos and their antimatter counterparts might mean that these particles violate a principle known as charge-parity (CP) symmetry -- meaning they don't behave exactly the same as their mirror opposites. Such a violation could explain why matter dominates the universe.
What the Results Show
The combined results from NOvA and T2K don't yet point decisively toward either mass ordering. If future studies confirm the normal ordering, scientists will still need more data to clarify whether CP symmetry is broken. But if the inverted ordering proves correct, this research suggests neutrinos could indeed violate CP symmetry, offering a powerful clue to why matter exists.
If neutrinos turn out not to violate CP symmetry, physicists would lose one of their strongest explanations for the existence of matter.
While these results don't solve the neutrino mystery outright, they expand what scientists know about these elusive particles and demonstrate the strength of international collaboration in physics.
The NOvA collaboration includes over 250 scientists and engineers from 49 institutions in eight countries. The T2K team involves more than 560 members from 75 institutions across 15 nations. The two groups began working together on this analysis in 2019, merging eight years of NOvA data with a decade of T2K results. Both experiments continue to collect new information for future updates.
"These results are an outcome of a cooperation and mutual understanding of two unique collaborations, both involving many experts in neutrino physics, detection technologies and analysis techniques, working in very different environments, using different methods and tools," T2K collaborator Tomáš Nosek said.
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