6 Jun 2017

The different rates of neutrino and antineutrino oscillations recorded by an international collaboration of researchers in Japan--including from Kavli IPMU--is an important step in the search for a new source of asymmetry in the laws that govern matter and antimatter.

The Standard Model of particle physics describes the basic building blocks of matter and how they interact. It also makes a point that for every particle created, there is an anti-particle. However, the Standard Model does not explain why our Universe still exists today, since the matter and anti-matter symmetry implies that matter--including galaxies, stars, and even humans--should have been annihilated by the equal amounts of anti-matter.
This violation of symmetry, called the charge-parity (CP) violation, has been observed experimentally, but not enough to explain the large amount of matter existing in the Universe.

The international T2K (Tokai-to-Kamioka) collaboration is the first experiment in the world that can search for CP violation by studying neutrino and anti-neutrino oscillations. High intensity beams of muon neutrinos (or muon anti-neutrinos) are produced at J-PARC (Japan Proton Accelerator Research Complex) on Japan’s east coast, and fired towards the Super-Kamiokande detector 295 km away in Gifu Prefecture. On the way, the neutrinos and anti-neutrinos spontaneously change 'flavor' from muon neutrinos or anti-neutrinos, to electron neutrinos or anti-neutrinos. A difference in the rates of oscillations in separate neutrino and anti-neutrino beams would be proof of an imbalance between particles and anti-particles, and that there is new physics to be learned beyond the Standard Model.

[Image]
The detected pattern of an electron neutrino candidate event observed by Super-Kamiokande.