Observation of the rare $B^0_s\to\mu^+\mu^-$ decay from the combined   analysis of CMS and LHCb data
  A joint measurement is presented of the branching fractions $B^0_s\to\mu^+\mu^-$ and $B^0\to\mu^+\mu^-$ in proton-proton collisions at the LHC by the CMS and LHCb experiments. The data samples were collected in 2011 at a centre-of-mass energy of 7 TeV, and in 2012 at 8 TeV. The combined analysis produces the first observation of the $B^0_s\to\mu^+\mu^-$ decay, with a statistical significance exceeding six standard deviations, and the best measurement of its branching fraction so far. Furthermore, evidence for the $B^0\to\mu^+\mu^-$ decay is obtained with a statistical significance of three standard deviations. The branching fraction measurements are statistically compatible with SM predictions and impose stringent constraints on several theories beyond the SM. 
The CMS and LHCb Collaborations: V. Khachatryan, A.M. Sirunyan, A.   Tumasyan, W. Adam, T. Bergauer, M. Dragicevic, J. Er\"o...
hep-ex hep-ph