Material-antimatter asymmetry observed for the first time in baryons

2025/07/16 Etxebeste Aduriz, Egoitz - Elhuyar Zientzia Iturria: Elhuyar aldizkaria

• Fisika

The asymmetry between matter and antimatter has been observed for the first time in baryons in the CERN LHCb experiment. This effect, known as load parietal tearing or CP tearing, is predicted by the Standard Model of Physics and was observed in mesons more than 60 years ago, but has not been observed so far in baryons, the particles that make up most of the matter in the universe. The discovery was published in the journal Nature.

According to cosmological models, matter and antimatter were produced in the same amount in the Big Bang. Then the matter and the antimatter were mutually annihilated and radiation was generated until the antimatter was exhausted. For some reason, some matter (and a lot of radiation) stagnated, and that matter makes up galaxies, stars, planets, and ourselves. It is believed that this imbalance was due to the existence of some difference in the behavior of matter and antimatter: Just a violation of the CP.

The CP violations that have been measured in the laboratory are consistent with the predictions of the Standard Model, but until now they were only observed in disintegrations of mesons, particles composed of a quark and an antiquark. Ordinary matter, however, consists of particles composed of three quarks (protons and neutrons) and electrons. By analyzing the data collected from proton collisions in LHC, it has been detected that baryons and antibaryons exhibit different disintegration behavior, i.e., CP violation occurs. In particular, it has been observed that there is a significant difference in the disintegration of the barium Lambda_b and its antibarium.

This CP violation was theoretically predicted, but it is not enough to explain the material-antimatter asymmetry of the Big Bang. In any case, the researchers emphasize that the experimental discovery of the details of this violation can offer important clues for new experiments and theoretical studies to understand the nature of the CP violation; as well as to look beyond the Standard Model.