Today, 23/3/2021, the LHCb experiment, at the Moriond International Conference, revealed a result which, if confirmed, would pose a serious problem to the well-established theory of fundamental interactions, the so-called Standard Model.
In nature there are three families of leptons: the electron with its positively charged partner, the positron; the muon (a kind of electron but 200 times heavier) also positive and negative and finally the tau, much heavier but with similar characteristics. Well, the Standard Model, apart from the difference in masses, predicts that the probability of decaying into a positive lepton and negative lepton pair is exactly identical for the three different flavors of leptons (e, mu, tau). This principle goes by the name of lepton universality.
The LHCb experiment compared two decays. In the first decay the charged B meson decays into a charged K meson plus an electron-positron pair, while in the second, the charged B meson decays into a charged K meson plus a pair of opposite charge muons. From the first results, it would seem that these two decays do not occur with the same probability, as predicted by the Standard model. The effect is small but quite evident, given that the probability that the experimental data are in agreement with the principle of lepton universality is currently 0.1%.
This probability, however small and encouraging, is still not sufficient to affirm with certainty a violation of the principle of lepton universality and other data are needed to confirm it. However, this is a very important clue to continue studying, especially in view of the next data collection campaign in the next future.
The extent of such a discovery, if confirmed, would be exceptional as it would be indicative of the existence of new physics beyond the Standard Model, opening up new and unexpected scenarios.
The Tor Vergata group participated in the construction of the experimental apparatus, in particular in the muon detector, and is currently involved in the analysis of the data collected and in the preparation of the next data collection campaign which foresees a substantial renewal of a large part of the detector.
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