LHCb: Search for the rare decays $B^0_s \to \mu^+\mu^-\mu^+\mu^-$ and $B^0 \to \mu^+\mu^-\mu^+\mu^-$ at LHCb

A search for the decays $B^0_s \to \mu^+\mu^-\mu^+\mu^-$ and $B^0 \to \mu^+\mu^-\mu^+\mu^-$ in a data sample of 1.0 inverse femtobarns collected with the LHCb detector in 2011 is discussed. In the SM, the non-resonant $B^0_s \to \mu^+\mu^-\mu^+\mu^-$ branching fraction is expected to be < 10$^{-10}$. One signal candidate is observed in the $B_d$ channel, and no signal candidates are observed in the $B_s$ channel. These observed events are consistent with the expected backgrounds and upper limits on the branching fractions are set at $\cal{B}(B^0_s \to \mu^+\mu^-\mu^+\mu^-) < 1.3 \times 10^{-8}$ and $\cal{B}(B^0 \to \mu^+\mu^-\mu^+\mu^-) < 5.4 \times 10^{-9}$ at 95 % CL.