The Experimental Neutrino Physics Group in the College of Arts and Sciences (A&S) has contributed to a groundbreaking study published in the journal Nature that brings scientists closer to answering one of physics’ most fundamental questions: Why does the Universe exist?

The study presents the first joint analysis combining data from the world’s two premier neutrino experiments—T2K (Tokai to Kamioka) in Japan and NOvA (NuMI Off-axis νe Appearance) in the United States. Associate Professor of Physics Denver Whittington and his students in A&S have been instrumental in multiple aspects of the NOvA experiment, from monitoring data quality to searching for exotic particles.

“I think this study was particularly valuable in that it identified and tackled a number of different challenges associated with comparing and combining measurements made from two very different neutrino experiments with different neutrino beams both looking to measure the same physics,” says Whittington, who has been part of the NOvA collaboration for more than a decade.

The Cosmic Mystery

The research addresses the baryon asymmetry problem: Why does our Universe contain almost entirely matter, with virtually no antimatter? Theory suggests the Big Bang created equal amounts of both 13.8 billion years ago. When these opposites meet, they destroy each other in bursts of energy. By that logic, the Universe should have self-destructed moments after its birth.

Scientists believe that matter and antimatter must have behaved slightly differently at some point—a broken symmetry that tipped the cosmic scales in favor of matter, allowing galaxies, stars, planets and life to exist. Neutrinos may hold the key.

Ghost Particles Under Study

Neutrinos are ghostly particles so tiny and reluctant to interact with ordinary matter that they can pass through the entire Earth without bumping into a single atom. These elementary particles come in three “flavors”—electron, muon and tau—and exhibit a quantum mechanical behavior called oscillation, spontaneously changing from one flavor to another as they travel.

T2K sends an intense beam of muon neutrinos 183 miles across Japan, while NOvA uses Fermilab’s NuMI beam to study neutrinos over a 500-mile path through the American Midwest. The NOvA collaboration includes more than 250 scientists and engineers from 49 institutions across eight countries.

Scientists first measure neutrinos at a near detector at the beam’s origin to establish a baseline. Then, as neutrinos travel vast distances and transform, massive detectors at the far end catch a tiny fraction and identify what type they’ve become, allowing scientists to calculate the precise rates and patterns of these transformations.

Both experiments share an ambitious goal: to measure how neutrinos and antineutrinos oscillate, and whether they oscillate differently. Finding that difference—called CP violation—could finally explain why the Universe favored matter over antimatter.

Solving a Puzzle

Before this joint analysis, NOvA slightly favored one value for CP violation while T2K pointed toward a different result. The solution lay in recognizing that each experiment had different strengths. T2K measurements excel at isolating the impact of CP violation, while NOvA has significant sensitivity to mass ordering—the question of which neutrino is heaviest.

By probing both experiments’ data simultaneously, the joint analysis leveraged these complementary strengths to demonstrate that both datasets were actually compatible, Whittington says.

Syracuse’s Contributions

Physics graduate student Aklima Lima is among the Syracuse group members involved in the collaboration. Her research has focused on data quality monitoring—ensuring that every neutrino event recorded meets rigorous standards. She has also worked on extending baseline neutrino event selection to boost the NOvA experiment’s physics sensitivity and explore cosmic-ray physics with the far detector in northern Minnesota.

Whittington serves as co-convener of a working group examining non-neutrino physics with the NOvA detectors, including searches for hints of dark matter and exotic hypothetical particles like magnetic monopoles.

3 Fundamental Questions

The joint analysis tackles questions that could reshape our understanding of the Universe: Can we definitively observe muon neutrinos oscillating into electron neutrinos? What is the ordering of neutrino masses—which type is heaviest and which is lightest? And do neutrinos violate the symmetry between matter and antimatter?

If antineutrinos oscillate at a different rate than neutrinos, it would be a smoking gun for CP violation—and a crucial clue to why we exist.

Looking Ahead

The DUNE facility, currently under construction in South Dakota, and Japan’s Hyper-Kamiokande detector will represent the next generation of neutrino experiments. The collaborative framework being established by T2K and NOvA will serve as a roadmap for these future projects.

As trillions of neutrinos continue their silent journey through our bodies and the Earth itself, the University’s physicists are working alongside scientists around the world to decode their secrets—and may finally answer fundamental questions about why our Universe exists.