$B^0_{s} \rightarrow \mu^+\mu^-$ at LHC
  Rare leptonic decays of $B_{(s)}^0$ mesons are sensitive probes of New Physics effects. A combination of the CMS and LHCb analyses on the search of the rare decays $B_{s}^0 \rightarrow \mu^+\mu^-$ and $B^0 \rightarrow \mu^+\mu^-$ is presented. The branching fractions of $B_{s}^0 \rightarrow \mu^+\mu^-$ and $B^0 \rightarrow \mu^+\mu^-$ are measured to be $\mathcal{B}(B_{s}^0 \rightarrow \mu^+\mu^-) = (2.8 \,^{+0.7}_{-0.6}) \times 10^{-9}$ and $\mathcal{B}(B^0 \rightarrow \mu^+\mu^-) = (3.9 \,^{+1.6}_{-1.4}) \times 10^{-10}$ respectively. A statistical significances of $6.2\,\sigma$ is evaluated for $B_{s}^0 \rightarrow \mu^+\mu^-$ from the Wilks' theorem while a significance of $3.0\, \sigma$ is measured for $B^0 \rightarrow \mu^+\mu^-$ from the Feldman-Cousins procedure. 
Flavio Archilli
hep-ex