10/22/2025
We recently combined forces with our friends on the T2K experiment to jointly analyse our data. This initial joint analysis provides some of the most precise neutrino-oscillation measurements in the field. It was published today in Nature.
T2K and NOvA are both long-baseline experiments: they each shoot an intense beam of neutrinos that passes through both a near detector close to the neutrino source and a far detector hundreds of miles away. Both experiments compare data recorded in each detector to learn about neutrinos’ behavior and properties. The experiments are complementary and provide the power to break degeneracies.
There are three remaining unknowns in the neutrino oscillation puzzle: the mass ordering, whether CP is violated – ie whether neutrinos and antineutrinos behave differently, and the octant of the 23 mixing angle. All of these affect the magnitude and energy dependence of the muon neutrino->electron neutrino appearance oscillation probability, and could affect electron neutrino appearance probability in antineutrinos differently.
NOvA and T2K both measure the appearance probabilities with different baselines and energies. This means the size of the effect of the mass ordering, in particular, is different between the two experiments. This provides one more way to tell the difference between the effects of CP violation and the mass ordering.
The combined results of NOvA and T2K do not favor either mass ordering. If future results show the neutrino mass ordering mass ordering is normal, NOvA’s and T2K’s results are less clear on CP symmetry, requiring additional data to clarify. However, if the neutrino mass ordering is found to be inverted, the results published today provide evidence that neutrinos violate CP symmetry, potentially explaining why the universe is dominated by matter instead of antimatter.
See the publication here: https://www.nature.com/articles/s41586-025-09599-3
