The quantum devil done it:
Particles obey a counter-intuitive but hugely successful theory called quantum mechanics. This theory shows that particles far too massive to be made directly in a lab collision can still influence what other particles do (through something called “quantum fluctuations”). Measurements of such effects are very complex, however, and much harder to explain to the public.
But recent results hinting at unexplained new physics beyond the standard model are of this second type. Detailed studies from the LHCb experiment found that a particle known as a beauty quark (quarks make up the protons and neutrons in the atomic nucleus) “decays” (falls apart) into an electron much more often than into a muon—the electron’s heavier, but otherwise identical, sibling. According to the standard model, this shouldn’t happen—hinting that new particles or even forces of nature may influence the process.
Intriguingly, though, measurements of similar processes involving “top quarks” from the ATLAS experiment at the LHC show this decay does happen at equal rates for electrons and muons.
Roger Jones, “The standard model of particle physics may be broken, expert says” at Phys.org (May 9, 2022)
You may also wish to read: Sabine Hossenfelder asks, did the W-boson break the Standard Model? Hossenfelder: Is it correct? I don’t know. It could be. But in all honesty, I am very skeptical that this result will hold up. More likely, they have underestimated the error and their result is actually compatible with the other measurements.