Standard Model Predictions for Rare K and B Decays without New Physics Infection

Understand

The Standard Model (SM) does not contain by definition any new physics (NP) contributions to any observable but contains four CKM parameters which are not predicted by this model.

• We point out that if these four parameters are determined in a global fit that includes processes which are infected by NP, the resulting SM contributions to rare decay branching ratios cannot be considered as true SM contributions to the latter.
• On the other hand true SM predictions, that are free from the CKM dependence, can be obtained for suitable ratios of the $K$ and $B$ rare decay branching ratios to $\Delta M_s$, $\Delta M_d$ and $|\varepsilon_K|$, all calculated within the SM.
• These three observables contain by now only small hadronic uncertainties and are already well measured so that rather precise true SM predictions for the ratios in question can be obtained.