Rare decays in B physics at CMS

Results on the angular analysis and differential branching fraction measurement of the decay B$^0\to$ K$^{*0}\mu^+\mu^-$ − are presented. The measurement of the forward-backward asymmetry of the muons, the K$^{∗0}$ longitudinal polarization fraction, and the differential branching fraction, as a function of the square of the dimuon system invariant mass, is reported. The results are in very good agreement with the Standard Model expectations. This analysis is performed using a data sample corresponding to an integrated luminosity of 5.2 fb$^{−1}$ collected with the CMS detector at the LHC in proton-proton collisions at $\sqrt s$ = 7TeV.