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

The differential branching fraction of the decay Λb0→Λμ+μ− is measured as a function of the square of the dimuon invariant mass, q2. A yield of 78±12Λb0→Λμ+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 q2 region above the square of the J/ψ mass, while at lower-q2 values upper limits are set on the differential branching fraction. Integrating the differential branching fraction over q2, while excluding the J/ψ and ψ(2S) regions, gives a branching fraction of B(Λb0→Λμ+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, Λb0→J/ψΛ, respectively