step closer to proving that b-meson decay violates lepton universality, a proof that may necessitate major changes to the Standard Model. As lead researcher on the most recent b-meson decay study, Prof. Mariusz Witek, said, “To put it in terms of the cinema, where we once only had a few leaked scenes from a much-anticipated blockbuster, the LHC has finally treated fans to the first real trailer.”
That trailer came in the form of a new examination of the data, which shows that the products of b-meson decay shoot off at angles different from those predicted within the Standard Model. The discrepancies in angle, along with the apparent deviations from the predicted rate of production of tau leptons and muons, may point to a break in lepton universality.
Since lepton universality is crucial to the Standard Model, and the Standard Model is crucial to our scientific understanding of matter, that evidence would necessitate a major paradigm shift.
This potential evidence has not been conclusively proven; the scientific paper, published in February in the Journal of High Energy Physics, puts the certainty of the results at a level well below what is necessary to call this a “discovery.” Dr. Marcin Chrząszcz, a physicist at the Institute of Nuclear Physics of the Polish Academy of Sciences and a lead author of the paper, explained, “We cannot talk of a discovery until the rate of accuracy rises to above 5 sigma.” At 5 sigma, the likelihood of the event occurring as a random coincidence is about one in 3.5 million. For the results of this experiment, that likelihood is about one in three thousand—enough to indicate that there may be a discrepancy, but not enough to serve as definitive proof.
Regardless of the uncertainty surrounding the b-meson decay inconsistencies, there are already hypotheses about what might cause them. The foremost hypothesis is the existence of an
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