Search for $B^{0}_{s} \to \mu^{+}\mu^{-}$ and $B^{0} \to \mu^{+}\mu^{-}$ decays with the CMS detector

The study of extremely rare or forbidden processes allows the indirect search for new physics through the comparison with the standard model expectations. The leptonic decays of $B^{0}_{s}$ and $B^{0}$ mesons are flavor changing neutral currents processes highly suppressed in the standard model, with small predicted branching fractions. A search for the rare decays $B^{0}_{s}\left(B^{0}\right)\to\mu^{+}\mu^{-}$ is performed in $pp$ collisions at $\sqrt{s} = 7$ Te\hspace{-.08em}V, with a data sample corresponding to an integrated luminosity of 5 $\text{fb}^{-1}$ collected by the CMS experiment at the LHC. The number of observed events is consistent with the background plus standard model signal expectation. The resulting upper limits on the branching fractions are ${\cal B}\left(B^{0}_{s}\to\mu^{+}\mu^{-}\right) < 7.7 \times 10^{-9}$ and ${\cal B}\left(B^{0}\to\mu^{+}\mu^{-}\right) < 1.8 \times 10^{-9}$ at $95\%$ confidence level.