Physicists from the LHCb collaboration refuted the previously found violation of the principle of lepton universality. The new analysis, which included a larger number of proton-proton collisions at the Large Hadron Collider, found no deviations in the decays of B mesons from the predictions of the Standard Model. The scientists devoted two articles to the results of their work, available on arXiv (1, 2). Briefly about them informs on its website European Organization for Nuclear Research.
What is the principle of lepton universality?
The properties and interactions of elementary particles are best described by the Standard Model, which is confirmed by numerous experiments. And according to it, the universe consists of 12 fundamental particles: six leptons and six quarks. They are classified according to three generations, which distinguish the particles from each other only by aroma and mass. However, the Standard Model still has some gaps and needs theories that will expand it – the so-called New Physics, which should be revealed, for example, in new particles or interactions between them.
One way to find a way out of the Standard Model is to compare experimental data from hadron decays with its predictions. And the principle of lepton universality predicted by the Standard Model fell under a possible hint of New Physics. He says that different leptons—electron, muon, and tau lepton—have the same strength of the electroweak interaction, and therefore should appear with the same probability in hadron decays. Its violation would indicate that there is, for example, some particle not predicted by the Standard Model, which affects the lepton in a different way. And experimental data brought hints of this violation.
Who violated this principle?
The peak of interest in the violation of the principle of lepton interaction fell on March 2021, when the collaboration of physicists LHCb presented preliminary results of his analysis of proton-proton collisions at the Large Hadron Collider. The scientists showed that the B meson chooses to decay into an electron-positron pair more often than into a muon-antimuon pair, although according to the Standard Model the decay rate should be the same. However, in the new results of the collaboration, the anomaly disappeared — the principle of lepton universality stood up to New Physics.
Violations will no longer be sought?
The anomaly in the data, which indicated a violation of lepton universality, disappeared when the data set was supplemented with data from the second season of operation of the Large Hadron Collider, which did not make it into the first stage of the study. In them, physicists considered two modes of B-meson decay at the same time, which made it possible to better monitor the background processes that contributed to the data. However, as the scientists write in their paper, additional data on particle decays may still challenge the Standard Model.
