Rare B decays at CMS

The flavour changing neutral current decays can be interesting probes for searching for New Physics. Angular distributions of the decay $\mathrm{B}^0 \to \mathrm{K}^{*0} \mu^ +\mu^-$ are studied using a sample of proton-proton collisions at $\sqrt{s} = 8~\mathrm{TeV}$ collected with the CMS detector at the LHC, corresponding to an integrated luminosity of $20.5~\mathrm{fb}^{-1}$. An angular analysis is performed to determine $P_1$ and $P_5'$, where $P_5'$ is of particular interest due to recent measurements that indicate a potential discrepancy with the standard model. Based on a sample of 1397 signal events, $P_1$ and $P_5'$ angular parameters are determined as a function of the dimuon invariant mass squared. The measurements are in agreement with standard model predictions.