Researchers from Stony Brook University’s Department of Physics and Astronomy have contributed to a joint analysis on neutrino oscillations, collaborating with international teams from the T2K (Tokai to Kamioka) and NOvA (NuMI Off-axis νe Appearance) experiments. The findings were published in Nature on October 22.
The collaboration combined data from both experiments, which use powerful accelerators and advanced detectors. By using the different experimental setups—T2K based in Japan and NOvA managed by Fermi National Accelerator Laboratory in the United States—the team achieved more precise measurements of neutrino oscillations. This effort reduced uncertainty in the differences between neutrino masses to less than 2 percent.
Despite this progress, the exact ordering of the three neutrino masses remains unresolved. However, the results provide strong constraints on Charge Conjugation and Parity (CP) symmetry violation depending on that ordering. Understanding CP symmetry violation is important for explaining why there is more matter than antimatter in the universe.
Chang Kee Jung, Distinguished Professor and chair of Stony Brook’s Department of Physics and Astronomy, said: “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.”
The study analyzed ten years’ worth of T2K data collected since 2010 along with six years’ worth of NOvA data starting from 2014. The effort demonstrates cooperation between two large international groups that have often been considered rivals but whose work is complementary.
While these initial results do not answer all questions about neutrinos, they improve scientists’ understanding significantly. Both experiments continue collecting data, with plans underway to update their combined analyses as new information becomes available.
The T2K collaboration includes over 560 members from 75 institutions across 15 countries—including several US universities such as 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—and receives support from the US Department of Energy.
NOvA consists of more than 250 scientists and engineers at 49 institutions across eight countries. Their active work on this joint analysis began in 2019.
NOvA and T2K remain the only currently operating long-baseline neutrino experiments worldwide. Their collaborative efforts have established groundwork for future research aiming to answer remaining questions about neutrinos.
