A search for the non-resonant decays $B^0_s \rightarrow \mu^{ +}\mu^{ -}\mu^{ +}\mu^{ -}$ and $B^0 \rightarrow \mu^{ +}\mu^{ -}\mu^{ +}\mu^{ -}$ is presented. The measurement is performed using the full Run 1 data set collected in proton-proton collisions by the LHCb experiment at the LHC. The data correspond to integrated luminosities of $1$ and $2~\mathrm{ fb}^{ -1}$ collected at centre-of-mass energies of $7$ and $8~\mathrm{ TeV}$, respectively. No signal is observed and upper limits on the branching fractions of the non-resonant decays at $95\%$ confidence level are determined to be \mathcal{ B}(B^0_s \rightarrow \mu^{ +}\mu^{ -}\mu^{ +}\mu^{ -}) & < 2.5 \times 10^{ -9} \mathcal{ B}(B^0 \rightarrow \mu^{ +}\mu^{ -}\mu^{ +}\mu^{ -}) & < 6.9 \times 10^{ -10}.
Categories: hep-ex