UC Irvine physicists measure two neutrino parameters with unprecedented precision

“Neutrinos are one of the fundamental particles comprising the universe. The findings mark the beginning of a broader program of measurements with critical implications for particle physics and astrophysics. In the United States, this research is funded by the National Science Foundation. Irvine, Calif., June 11, 2026 — Electrons, protons and neutrons comprise all the atoms that make up the universe. Another particle, the neutrino, is less understood than its atomic counterparts, but that is changing. In a new study co-led by University of California, Irvine scientists, a team reports the most precise measurements ever made of two neutrino parameters at a new neutrino detector in China called the Jiangmen Underground Neutrino Observatory, or JUNO. “We’re turning on this very, very precise instrument called JUNO for the first time after over a decade of design and construction. It’s really exciting ,” said Pedro Ochoa-Ricoux, a UC Irvine particle physicist and lead author of the study, which was featured on the cover of the prestigious Nature journal. “The main thing about these first results from JUNO is the precision of our measurements. With our first sixty days of data, we achieved a precision surpassing that achieved over two decades of previous measurements.” The parameters the team measured relate to a neutrino’s oscillation – a phenomenon that indicates that neutrinos have mass. It’s still unclear, though, which neutrino is the heaviest and which is the lightest – a question known as the neutrino mass ordering. “We still don’t know the neutrino mass ordering,” said Sindhujha Kumaran, a postdoctoral researcher in Ochoa-Ricoux’s group. “One of the main goals of JUNO is to figure that out.” JUNO, Kumaran added, is especially equipped to tackle the problem. “With this detector, you can see tiny differences in the oscillation pattern imprinted on the energy spectrum of the neutrinos emitted by eight nuclear reactors that will tell you which mass is the heaviest, or the lightest,” Kumaran said. “No other experiment can do it this way”. The neutrino mass ordering may still be unknown, but the new work demonstrates that JUNO will be able to deliver results that will be an order of magnitude more precise than current measurements in some cases, according to Ochoa-Ricoux. “Our group at UC Irvine played a leading role in these new results,” he said. Ochoa-Ricoux is one of the coordinators of the analysis group responsible for producing the results, and Kumaran co-led one of the three analysis teams that carried out the study. The UC Irvine team, which over the years has also included many undergraduate students, graduate students and engineers, has been involved in the experiment since the beginning and holds important responsibilities in its leadership, as well as in its design and construction. The research will also illuminate the role neutrinos play in the universe. By improving our understanding of neutrino properties, including their masses, scientists can better test ideas about the origin and evolution of the universe, including theories that seek to explain why matter dominates over antimatter. “It’s the advent of a new era of precision neutrino physics,” said Ochoa-Ricoux, who explained how UC Irvine is the only institution in the United States that has a full membership status with JUNO. UC Irvine has a long history of neutrino research excellence. In 1995, Frederick Reines, the founding dean of the School of Physical Sciences, won the Nobel Prize in Physics for the discovery of the neutrino . Funding sources includethe National Science Foundation (NSF-PHY-2411802), as well as the University of California. About the University of California, Irvine: Founded in 1965, UC Irvine is a member of the prestigious Association of American Universities and is ranked among the nation’s top 10 public universities by U.S. News & World Report . The campus has produced five Nobel laureates and is known for its academic achievement, premier research, innovation and anteater mascot. Led by Chancellor Howard Gillman, UC Irvine has more than 36,000 students and offers 224 degree programs. It’s located in one of the world’s safest and most economically vibrant communities and is Orange County’s second-largest employer, contributing $7 billion annually to the local economy and $8 billion statewide. For more on UC Irvine, visit www.uci.edu . Media access: Radio programs/stations may, for a fee, use an on-campus studio with a Comrex IP audio codec to interview UC Irvine faculty and experts, subject to availability and university approval. For more UC Irvine news, visit news.uci.edu . Additional resources for journalists may be found at https://news.uci.edu/media-resources .

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