Item

Abstract

The Λ_b⁰ → 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⁻K_S⁰ decay as a reference channel, the product of the relative production cross-section and decay branching fractions is measured to be

R = (^σΛ_b⁰ / ^σB⁰) × (B(Λ_b⁰ → D⁺D⁻Λ)) / (B(B⁰ → D⁺D⁻K_S⁰)) = 0.179 ± 0.022 ± 0.01,

where the first uncertainty is statistical and the second is systematic. The known branching fraction of the reference channel, B(B⁰ → D⁺D⁻K_S⁰), and the cross-section ratio, ^σΛ_b⁰ / ^σB⁰ , previously measured by LHCb are used to derive the branching fraction of the Λ_b⁰ → D⁺D⁻Λ decay

B(Λ_b⁰ → 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⁻K_S⁰) and ^σΛ_b⁰ / ^σB⁰, respectively. Inspection of the D⁺Λ and D⁺D⁻ invariant-mass distributions suggests a rich presence of intermediate resonances in the decay. The Λ_b⁰ → D^∗+D⁻Λ decay is also observed for the first time as a partially reconstructed component in the D⁺D⁻Λ invariant mass spectrum.