Researchers at Indiana University have helped make a significant advance in our understanding of the universe through a partnership between two leading international neutrino experiments. Neutrinos are extremely small, nearly massless particles that constantly pass through space, planets, and even our bodies, yet rarely interact with anything. Findings published in the journal Nature move scientists closer to answering a profound question: why does the universe contain matter such as stars, planets, and life instead of being empty?
The breakthrough comes from an unprecedented joint analysis of data from the NOvA experiment in the United States and T2K in Japan. These two long distance neutrino projects are among the most sophisticated of their kind. By combining their results, researchers can better study neutrinos and their antimatter counterparts, offering insight into why the universe did not self destruct immediately after the Big Bang.
In both experiments, scientists generate beams of neutrinos using particle accelerators and send them across vast underground distances to massive detectors. Detecting them is extraordinarily difficult. Out of countless particles produced, only a tiny fraction leave measurable signals. Advanced detectors and powerful software are then used to reconstruct these rare interactions and study how neutrinos change as they travel.
Indiana University has played a major role in this work for decades. IU scientists have contributed to building detector systems, interpreting data, and mentoring young researchers. Mark Messier, Distinguished Professor and Chair of the Physics department within the College of Arts and Sciences at IU Bloomington, has held leadership roles in the project since 2006. Other IU researchers involved include physicists Jon Urheimand James Musser (Emeritus), Astronomy Professor Stuart Mufson (Emertius), and Jonathan Karty in the Chemistry department in the College at IU.
Neutrinos and the Matter Antimatter Mystery
Neutrinos are among the most common particles in the cosmos. They carry no electric charge and have almost no mass, which makes them incredibly difficult to detect. That same property, however, makes them invaluable tools for probing the deepest laws of physics.
One of the greatest puzzles in cosmology is why the universe is dominated by matter. The Big Bang should have created equal amounts of matter and antimatter. When matter and antimatter meet, they annihilate each other in a burst of energy. If the early universe had contained perfectly equal amounts of both, everything would have disappeared. Instead, a slight imbalance favored matter, allowing galaxies, stars, planets, and life to form.
Scientists believe neutrinos may help explain that imbalance. Neutrinos exist in three varieties, or “flavors,” known as electron, muon, and tau. As they move through space, they can switch from one flavor to another in a process called oscillation. If neutrinos and antineutrinos oscillate differently, that difference could point to why matter ultimately prevailed.
NOvA and T2K Join Forces
The new Nature study stands out because it merges data from two premier neutrino observatories. NOvA (the NuMI Off-axis νe Appearance experiment) sends a neutrino beam 810 kilometers from the Fermi National Accelerator Laboratory near Chicago to a 14,000-ton detector in Ash River, Minnesota. Meanwhile, Japan’s T2K project fires a beam 295 kilometers from the J-PARC accelerator in Tokai to the massive Super-Kamiokande detector beneath Mount Ikenoyama.
By analyzing their results together, researchers improved their ability to measure how neutrinos behave. According to a press release from Nature, “Combining the analyses takes advantage of the complementary sensitivities of the two experiments and demonstrates the value of collaboration.” NOvA’s longer distance through Earth and T2K’s shorter but more intense beam provide complementary strengths, allowing scientists to compare and refine their measurements with exceptional precision.
Pooling the datasets enabled the teams to better determine the parameters that control neutrino oscillations, particularly those related to differences between neutrinos and antineutrinos. The results focus on CP symmetry (charge-parity symmetry), the principle that matter and antimatter should follow identical physical laws, behaving as mirror images of each other.
Yet the observable universe is overwhelmingly made of matter, with very little antimatter remaining from the Big Bang. The combined findings suggest there may be a difference in how neutrinos and antineutrinos oscillate, indicating a possible violation of CP symmetry. In simple terms, neutrinos may not behave exactly like their antimatter counterparts. That subtle distinction could be a crucial clue to why matter survived.
“We’ve made progress on this really big, seemingly intractable question: why is there something instead of nothing?” said Professor Messier. “And, we’ve set the stage for future research programs that aim to use neutrinos to tackle other questions.”
Technology, Training, and Global Collaboration
Large scale particle physics experiments often produce benefits beyond fundamental science. Technologies developed to detect neutrinos, including high speed electronics and advanced data analysis systems, often find practical applications in industry. The joint research effort is supported by funding from the U.S. Department of Energy.
“There has been transformative technological innovation across all sectors of society that’s come out of high-energy physics,” noted Messier. “Further, next-generation scientists immerse themselves in data science, in machine learning, artificial intelligence, and in electronics, and then go into industries with the deep skills they’ve gained while trying to answer these really difficult questions.”
The NOvA and T2K collaborations involve hundreds of scientists from more than a dozen countries across the United States, Europe, and Japan. Their shared analysis demonstrates the scientific power of international cooperation.
IU Ph.D. students currently contributing to the joint study include Reed Bowles, Alex Chang, Hanyi Chen, Erin Ewart, Hannah LeMoine, and Maria Manrique-Plata. Since NOvA began in 2014, Messier and his colleagues have also mentored many IU graduate and undergraduate students working on the experiment.
The partnership offers a preview of how future large particle physics projects may operate. For Indiana University and its collaborators, the results open the door to even more precise studies that build on this work.
“As a physicist I find it fascinating that a huge question, like why there’s matter in the universe instead of antimatter, can be broken down into smaller, step-by-step questions,” said Messier. “Instead of being dumbstruck by the enormity of it, we can actually make progress toward an answer about why we’re here in the universe.”