Observation of the suppressed decay $\Lambda^{0}_{b}\rightarrow p\pi^{-}\mu^{+}\mu^{-}$

The suppressed decay Λ$_{b}^{0}$ → pπ$^{−}$ μ$^{+}$ μ$^{−}$, excluding the J/ψ and ψ(2S) → μ$^{+}$ μ$^{−}$ resonances, is observed for the first time with a significance of 5.5 standard deviations. The analysis is performed with proton-proton collision data corresponding to an integrated luminosity of 3 fb$^{−1}$ collected with the LHCb experiment. The Λ$_{b}^{0}$ → pπ$^{−}$ μ$^{+}$ μ$^{−}$ branching fraction is measured relative to the Λ$_{b}^{0}$ → J/ψ(→μ$^{+}$ μ$^{−}$)pπ$^{−}$ branching fraction giving $ \frac{\mathrm{\mathcal{B}}\left({\Lambda}_b^0\to p{\pi}^{-}{\mu}^{+}{\mu}^{-}\right)}{\mathrm{\mathcal{B}}\left({\Lambda}_b^0\to \mathrm{J}/\psi \left(\to {\mu}^{+}{\mu}^{-}\right)p{\pi}^{-}\right)}=0.044\pm 0.012\pm 0.007, $ where the first uncertainty is statistical and the second is systematic. This is the first observation of a b → d transition in a baryonic decay.