Japanese physicists have studied the cause of baryon asymmetry is the violation of symmetry between matter and antimatter that could explain why the Universe exists at all substance. They managed to reveal the most convincing to date, the evidence that the imbalance arose due to the behavior of neutrinos. Article scientists published in the journal Nature.
The researchers observed oscillations of neutrinos within the T2K experiment (Tokai to Kamioka). Neutrino oscillations are a phenomenon in which neutrinos change their grade. In this case, the physicists were interested in the transition of muon neutrinos and muon antineutrinos in their “mirror” shape — electron neutrino and electron antineutrino, respectively.
One of the necessary conditions for the predominance of matter over antimatter that is observed in the modern Universe is the symmetry-breaking charge-parity (CP symmetry), that is, the laws of physics remain the same for particles which are turned into corresponding antiparticles and simultaneously mirrored. The violation of CP symmetry was observed for the quarks, but the magnitude of this violation was insufficient to explain the baryon asymmetry. T2K is designed to search for CP violation in neutrino oscillations.
During the T2K beam of muon neutrinos and antineutrinos generated in the proton accelerator complex J-PARC, near the village of Tokai on the East coast of Japan. Particles overcame 295 kilometers and recorded neutrino detector “Super-Kamiokande” in mine Kamioka. However, their grade could change in the course of neutrino oscillations.
The degree of symmetry breaking is determined by the parameter δ, which can take values from -180 degrees to 180 degrees. If the parameter is equal to zero or 180 degrees, then neutrinos and antineutrinos will change your grade in a similar way, without violating CP-symmetry. However, δ may enhance oscillations of neutrinos or antineutrinos, taking values of -90 degrees or 90 degrees, respectively. The researchers made allowances for the increased oscillations, due to the fact that the detectors are made of matter and not antimatter.
The results obtained to the greatest extent consistent with the value δ = -90 degrees, and the smallest in the range of 2 to 165 degrees at the level of statistical significance at the 99.7 per cent, which corresponds to three Sigma, or three standard deviations. At the same time, the sensitivity of the experiment is insufficient for accurate determination of whether violated CP-symmetry or not. This requires a statistical significance corresponding to five Sigma. In the future, scientists are going to upgrade the experimental setup.
