Measurement of the differential branching fraction of the decay Λb0→Λμ+μ-

Abstract The differential branching fraction of the decay Λ b 0 → Λ μ + μ − is measured as a function of the square of the dimuon invariant mass, q 2 . A yield of 78 ± 12 Λ b 0 → Λ μ + μ − decays is observed using data, corresponding to an integrated luminosity of 1.0 fb − 1 , collected by the LHCb experiment at a centre-of-mass energy of 7 TeV. A significant signal is found in the q 2 region above the square of the J / ψ mass, while at lower- q 2 values upper limits are set on the differential branching fraction. Integrating the differential branching fraction over q 2 , while excluding the J / ψ and ψ ( 2 S ) regions, gives a branching fraction of B ( Λ b 0 → Λ μ + μ − ) = ( 0.96 ± 0.16 ( stat ) ± 0.13 ( syst ) ± 0.21 ( norm ) ) × 10 − 6 , where the uncertainties are statistical, systematic and due to the normalisation mode, Λ b 0 → J / ψ Λ , respectively.