Observation of the suppressed decay Λb0 → pπ−μ+μ

A bstract The suppressed decay Λ b 0 → pπ − μ + μ − , excluding the J/ ψ and ψ (2 S ) → 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 ℬ Λ b 0 → p π − μ + μ − ℬ Λ b 0 → J / ψ → μ + μ − p π − = 0.044 ± 0.012 ± 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.