The Large Hadron Collider at CERN has found anomalies in the decay of b-hadrons (heavy particles containing a bottom quark).

The 'Standard Model' predicts (with almost no margin of error) that when bottom quarks (a.k.a. 'beauty quarks') decay, the products should contain equal numbers of electrons and muons. But the experimental measurements of results of such decays (bottom quarks are produced in vast quantities in CERN experiments) the ratio is not equal.

The observed value differs from unity by 2.6 standard deviations, less than the 5 standard deviations particle physicists require before claiming a discovery. Yet, if substantiated by further data, the finding would imply a striking breakdown of the standard model and clear evidence for a new kind of interaction that violates lepton universality—a surprising and view-changing discovery.

See : A Challenge to Lepton Universality, Physics 7, 102.

To quantum physicists, the anomaly is so striking that some have suggested that it hints at as-yet-unknown physics - some alluding to a so-called "5th force" as a possible explanation. (See : BBC News, 2021)

Experiments are underway at CERN's LHCb experiment, and in the newly revamped LHC which will start running new tests in late 2022.