Researchers from Stony Brook University have participated in a joint analysis with teams from the T2K (Tokai to Kamioka) and NOvA (NuMI Off-axis νe Appearance) neutrino experiments. This collaboration brought together data from both experiments, which use advanced accelerators and detectors to study long-baseline neutrino oscillations. By combining the different baselines and energy spectra of T2K and NOvA, the team was able to improve the precision of measurements related to neutrino oscillations. The findings will be published in Nature on October 22, 2025.
The joint analysis reduced the uncertainty in the differences between neutrino masses to less than 2%. While the exact ordering of the three neutrino masses remains unknown, the results indicate that the extent of Charge Conjugation and Parity (CP) symmetry violation—differences in behavior between particles and antiparticles—can be more strongly constrained depending on this ordering.
This collaborative work is seen as a significant step toward understanding CP symmetry violation in neutrinos and the origin of the matter–antimatter asymmetry in the universe. The analysis included ten years of T2K data since 2010 and six years of NOvA data since 2014, highlighting the value of cooperation between two international experiments that have been considered both competitive and complementary.
Chang Kee Jung, Distinguished Professor and Chair of the Department of Physics and Astronomy at Stony Brook University, commented on the collaboration: “I truly commend both NOvA and the T2K collaborations seeing this through despite many technical and political challenges during the joint analysis process. The initial discussion of a possible joint analysis started more than 10 years ago and the first NOvA-T2K meeting was held in March 2016. Thus, it has been a really long process. The outstanding and informative results obtained from this joint analysis are products of strong desires of both collaborations to maximize the scientific output from their experiments in advancing human knowledge. It is an exemplary model of inter-experimental collaboration. Stony Brook has been the Principal Investigator institution for the T2K United States group since the inception of the T2K experiment and has made numerous and significant contributions to the experiment, including this joint analysis.”
Although these first results do not answer all outstanding questions about neutrinos, they provide more detailed information for physicists and demonstrate the effectiveness of the collaboration between T2K and NOvA.
The T2K collaboration includes more than 560 members from 75 institutions across 15 countries. Other U.S. institutions involved are Boston University; Duke University; Lawrence Berkeley National Laboratory; Louisiana State University; Michigan State University; South Dakota School of Mines and Technology; Stanford Linear Accelerator Center (SLAC); University of California, Irvine; University of Colorado, Boulder; University of Houston; University of Minnesota; University of Pennsylvania; University of Pittsburgh; and University of Rochester. The U.S. group’s participation is supported by the U.S. Department of Energy.
NOvA is managed by Fermi National Accelerator Laboratory and consists of over 250 scientists and engineers from 49 institutions in eight countries. The collaboration began work on this joint analysis in 2019. Both T2K and NOvA continue to collect data, with plans to update the analysis as new information becomes available.
Currently, T2K and NOvA are the only operating long-baseline neutrino experiments. Their initial combined results provide a foundation for future research that aims to resolve remaining questions about neutrinos.