First observation of the Λ⁰b → D⁺ D⁻ Λ decay

The Λ⁰b → D⁺ D⁻ Λ decay is observed for the first time using proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.3 fb⁻¹. Using the B⁰ → D⁺ D⁻ KS⁰ decay as a reference channel, the product of the relative production cross-section and decay branching fractions is measured to be R=σΛ⁰bσB⁰ × B(Λ⁰b → D⁺ D⁻ Λ) B(B⁰ → D⁺ D⁻ KS⁰)=0.179 ± 0.022 ± 0.014 where the first uncertainty is statistical and the second is systematic. The known branching fraction of the reference channel, B(B⁰ → D⁺ D⁻ KS⁰), and the cross-section ratio, σΛ⁰b / σB⁰, previously measured by LHCb are used to derive the branching fraction of the Λ⁰b → D⁺ D⁻ Λ decay B(Λ⁰b → D⁺ D⁻ Λ)=(1.24 ± 0.15 ± 0.10 ± 0.28 ± 0.11) × 10⁻⁴, where the third and fourth contributions are due to uncertainties of B(B⁰ → D⁺ D⁻ KS⁰) and σΛ⁰b / σB⁰, respectively. Inspection of the D⁺ Λ and D⁺ D⁻ invariant-mass distributions suggests a rich presence of intermediate resonances in the decay. The Λ⁰b → D*+ D⁻ Λ decay is also observed for the first time as a partially reconstructed component in the D⁺ D⁻ Λ invariant mass spectrum.