First observation of $B^{+} \rightarrow \pi^{+} \mu^{+} \mu^{-}$

A search for the decay $B^{+} \rightarrow \pi^{+} \mu^{+} \mu^{-}$ is presented using 1.0 fb$^{-1}$ of pp collision data integrated luminosity collected with the LHCb experiment at the Large Hadron Collider during 2011. This decay is observed for the first time with 5.2 $\sigma$ significance, at a branching fraction $\cal {B}$(B$^{+} \rightarrow \pi^{+} \mu^{+} \mu^{-}$) = (2.4 $\pm$ 0.6 (stat)$\pm$ 0.2 (syst))x 10$^{-8}$.