HEP In the literature: contested

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

In plain words

After a well-known hint was withdrawn in 2022, some B decays to muon pairs still occur less often, or with different angular patterns, than predicted.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.

Precise statement

Branching ratios of $B \to K \mu \mu$ and $B_{s} \to \phi \mu \mu$ at low $q^{2}$ and the angular observable $P5'$ in $B \to K* \mu \mu$ deviate from SM predictions by about 2 to 4 sigma, while $R_{K}$ and $R_{K}*$ agree with the SM (LHCb, 2022). Identify whether a shift in the Wilson coefficient $C_{9}$ is short-distance new physics or long-distance c-cbar loops.

What would settle it

Data-driven determination of the $q^{2}$ dependence of non-local charm contributions from LHCb Run 3 and Belle II, combined with lattice form factors.