In the April 15, 2020 issue of Nature magazine, members of the international collaborative research project “T2K collaboration (T2K: Tokai-to-Kamioka)” announced an excellent achievement in research in an article titled “Constraint on the matter-antimatter symmetry-violating phase (CP symmetry breakage) in neutrino oscillations”. Included in the paper’s co-authors are Professor Yoshihiro Seiya and Associate Professor Kazuhiro Yamamoto of the High Energy Physics Laboratory of the Graduate School of Science.

T2K(Tokai to Kamioka)is a neutrino oscillation experiment designed to study how neutrinos change during flight. In June 2011, the T2K experimental group announced that they were the first in the world to obtain experimental evidence of an oscillation phenomenon where muon neutrinos change to electron neutrinos. About 500 members from 69 universities and research institutions in 12 countries are participating in this on-going experiment.

In this paper, the oscillation differences between muon neutrinos changing to electron neutrinos and muon antineutrinos changing to electron antineutrinos were measured at a 99.7% confidence level, indicating a CP symmetry breakage in neutrinos at a 95% confidence level. This indicates that there is a difference in the behavior of neutrinos and antineutrinos, which are the basis for the matter-antimatter relationship, and can act as a possible clue to clarify the reason why matter becomes dominant over antimatter in the formation of the universe.

[Image of a candidate electron neutrino reaction event and electron antineutrino reaction event observed in the Super-Kamiokande of the T2K experiment]

Related Link

[Journal] Nature (Posted April 15, 2020)
[Article title] Constraint on the matter–antimatter symmetry-violating phase in neutrino oscillations
[URL] https://www.nature.com/articles/s41586-020-2177-0