Recent CMS Results on Rare Heavy Flavour Decays

Recent results on the B hadron decays from the CMS experiment at the LHC are reported. The observation of the \({{\textrm{B}}^{0}}\to{\psi\textrm{(2S)}}{{\textrm{K}}^{0}_{\textrm{S}}}{{{\pi}^{+}{\pi}^{-}}}\) and \({{\textrm{B}}^{0}_{\textrm{s}}}\to{\psi\textrm{(2S)}}{{\textrm{K}}^{0}_{\textrm{S}}}\) decays is presented together with the first observation of the \(\eta\to\mu^{+}\mu^{-}\mu^{+}\mu^{-}\) decay and the first observation of the \({\Lambda^{0}_{\textrm{b}}}\to{\textrm{J}/\psi}{\Xi^{-}}{{\textrm{K}}^{+}}\) decay. The results are based on data sample collected in pp collisions at 13 TeV.