New results on the search for $B_s^0\to {\mu }^{+}{\mu }^{-}$ from LHCb

A search for the rare decays $B_s^0\to {\mu }^{+}{\mu }^{-}$ and $B^0\to {\mu }^{+}{\mu }^{-}$ is performed with the LHCb experiment using 1.1,fb${}^{-1}$ of data collected at $\sqrt{s}=8$,TeV$and1.0fb$^{-1}$ of data collected at $\sqrt{s}=7$,TeV. An excess of $B_s^0\to {\mu }^{+}{\mu }^{-}$ candidates with respect to the background expectations is observed with a statistical significance of 3.5 standard deviations. A branching fraction of $\mathcal{B}\mathcal{R}(B_s^0\to {\mu }^{+}{\mu }^{-})=(3.2_{-1.2}^{+1.5})\times {10}^{-9}$ is measured with an unbinned maximum likelihood fit. The measured branching fraction is in agreement with the expectation from the Standard Model. The observed number of $B^0\to {\mu }^{+}{\mu }^{-}$ candidates is consistent with the background expectation and an upper limit on the branching fraction of $\mathcal{B}\mathcal{R}(B^0\to {\mu }^{+}{\mu }^{-})<9.4\times {10}^{-10}$ is obtained.