Revealed the reason for the existence of matter in the Universe

Revealed the reason for the existence of matter in the Universe
Revealed the reason for the existence of matter in the Universe

Japanese physicists have studied the cause of baryon asymmetry - a violation of symmetry between matter and antimatter, which could explain why matter exists in the universe at all. They uncovered the most compelling evidence to date that the imbalance was due to the behavior of neutrinos. The article of scientists was published in the journal Nature.

The researchers observed neutrino oscillations in the T2K (Tokai to Kamioka) experiment. Neutrino oscillations are a phenomenon in which neutrinos change their kind. In this case, physicists were interested in the transition of muon neutrinos and muon antineutrinos into their "mirror" forms - electron neutrinos and electron antineutrinos, respectively.

One of the necessary conditions for the predominance of matter over antimatter, which is observed in the modern Universe, is the violation of charge-parity symmetry (CP-symmetry), that is, the laws of physics do not remain unchanged for particles that have been turned into corresponding antiparticles and at the same time mirrored. Breaking of CP symmetry was observed for quarks, but the magnitude of this breaking turned out to be insufficient to explain the baryon asymmetry. T2K is designed to search for CP violation in neutrino oscillations.

During T2K, a beam of muon neutrinos and antineutrinos was generated at the J-PARC proton accelerator complex near the village of Tokai on the east coast of Japan. The particles traveled 295 kilometers and were recorded by the Super-Kamiokande neutrino detector in the Kamioka mine. Moreover, their sort 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 their kind in a similar way, without breaking the CP symmetry. However, δ can enhance neutrino or antineutrino oscillations, taking values of -90 degrees or 90 degrees, respectively. The researchers adjusted for the amplification of the oscillations caused by the fact that the detectors are made of matter, not antimatter.

The results obtained were most consistent with a δ value of -90 degrees, and at the least - in the range from 2 to 165 degrees at a statistical significance level of 99.7 percent, which corresponds to three sigma, or three standard deviations. At the same time, the sensitivity of the experiment is not yet sufficient to accurately determine whether the CP symmetry is broken or not. This requires five sigma statistical significance. In the future, scientists are going to modernize the experimental installations.

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