Observation of the suppressed decay Λ b 0 → pπ - μ + μ -

Abstract

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\to p{π}^{-/μ+{μ}-)}{B({Λ}_b^0\to J/ψ (\to {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.