Search for the rare decay $B^{+} \rightarrow \mu^{+}\mu^{-}\mu^{+}\nu_{\mu}$

A search for the rare leptonic decay $B^{+} \rightarrow \mu^{+}\mu^{-}\mu^{+}\nu_{\mu}$ is performed using proton-proton collision data corresponding to an integrated luminosity of $4.7$ fb$^{-1}$ collected by the LHCb experiment. The search is carried out in the region where the lowest of the two $\mu^{+}\mu{-}$ mass combinations is below $980$ MeV/$c^{2}$. The data are consistent with the background-only hypothesis and an upper limit of $1.6 \times 10^{-8}$ at 95\% confidence level is set on the branching fraction in the stated kinematic region.