Flavor anomalies: CKM unitarity and B decays

4 problems

• Is the Belle II $B\,\mathrm{to}\,K\,\nu\,\nu$ excess real?

  Open

  Belle II found that B mesons decay to a kaon plus invisible particles more often than expected, about four times the predicted rate. It could be new particles or a fluctuation.

• Are $b \text{ to } s \mu \mu$ tensions new physics or charm-loop effects?

  Contested

  After a well-known hint was withdrawn in 2022, some B decays to muon pairs still occur less often, or with different angular patterns, than predicted. Whether hard-to-compute strong-force effects explain this is disputed.

• Is first-row CKM unitarity violated (Cabibbo angle anomaly)?

  Open

  The probabilities for an up quark to turn into each kind of down-type quark should add to exactly one. Current data fall short by about a tenth of a percent, roughly 3 standard deviations.

• Is lepton flavor universality violated in $b\,\mathrm{to}\,c\,\tau\,\nu$ decays?

  Open

  The SM treats electrons, muons and taus alike except for mass. B meson decays to $\tau$ leptons occur more often than predicted, by more than 3 standard deviations.