The T2K experiment uses a beam consisting of muon neutrinos or muon antineutrinos produced at the Japan Proton Accelerator Research Complex (J-PARC) located in Tokai on the east coast of Japan. A small portion of these neutrinos (or antineutrinos) is detected at a distance of 295 km at the Super-Kamiokande detector, located under a mountain in Kamioka, near the west coast of Japan. For this purpose, the neutrino interaction in the huge tank of ultraclean water and the resulting so-called Cherenkov radiation are used. The experiment proved that some of the neutrinos traversing the distance oscillate, i.e. they change their type to electron neutrinos or antineutrinos.

The T2K experiment, whose previous results confirmed the phenomenon of neutrino oscillation (awarded the Nobel Prize in 2015), focuses on, among others, the study of the phenomenon of matter/antimatter symmetry violation in neutrino oscillations. This is an important step towards explaining one of the fundamental mysteries of the universe — the domination of matter over antimatter. The parameter governing the matter/antimatter symmetry breaking in neutrino oscillation, called δCP phase, can take a value from -180º to 180º. For the first time, with a very high probability (at the 99.7% confidence level), T2K has excluded almost half of the possible values of the δCP parameter, thus revealing a basic property of neutrinos which has not been measured until now.

You can find out more about the research from the article on the “Nature” website and in the introductory article.

[1] Abe, K., Akutsu, R., Ali, A. et al. Constraint on the matter–antimatter symmetry-violating phase in neutrino oscillations. Nature 580,339–344 (2020). https://doi.org/10.1038/s41586-020-2177-0