Search for the rare decays $B^0_{(s)} \to \mu^+ \mu^-$ at LHCb

A search for the $B_s \to \mu^+ \mu^-$ and $B_d \to \mu^+ \mu^-$ decays is presented using $\sim$ 300 pb$^{-1}$ of $pp$ collisions at $\sqrt{s}$ = 7 TeV collected by the LHCb experiment at the Large Hadron Collider at CERN. The measured upper limit for the branching ratio of the $B_s \to \mu^+ \mu^-$ decay is $\cal B(B_s \to \mu^+ \mu^-$ < 1.3 (1.6) x 10$^{-8}$ at 90 % (95%) confidence level (CL), while in the case of the $B_d \to \mu^+ \mu^-$ decay the measured upper limit is $\cal B(B_d \to \mu^+ \mu^-$ < 4.2 (5.1) x 10$^{-9}$ at 90 % (95%) CL. A combination with the 2010 dataset results in $\cal B(B_s \to \mu^+ \mu^-$ < 1.2 (5.1) x 10$^{-8}$ at 90 % (95%) CL.