Search for new physics in $B_s \rightarrow \mu^+ \mu^-$ and $B \rightarrow K^{(*)} \mu^+ \mu^-$

Transitions of the type $b \to s l^+ l^-$ are flavour changing neutral current processes where new physics can enter in competing loop diagrams with respect to the Standard Model contributions. In these decays several observables sensitive to new physics, and where theoretical uncertainties are under control, can be constructed. Particularly interesting are the angular asymmetries in the decay $B_d \to K^* \mu^+ \mu^-$ and the measurement of the branching fraction of the decays $B_{s,d} \to \mu^+ \mu^-$. Recent measurements of these observables and the measurement of the isospin asymmetry in the decays $B \to K^{(*)} \mu^+ \mu^-$ are presented.