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.
Categories: hep-ex