First observation of the Λb⁰ → D+D−Λ decay

A bstract The Λb⁰ Λ b 0 → 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 B 0 → D⁺D⁻KS⁰ D + D − K S 0 decay as a reference channel, the product of the relative production cross-section and decay branching fractions is measured to be $$ R={σΛ_b^0}{σB^0}={B({Λ}_b^0→ {D}⁺{D}⁻Λ )}{B({B}^0→ {D}⁺{D}⁻{K}S^0)}=0.179± 0.022± 0.014, $$ R = σ Λ b 0 σ B 0 = B Λ b 0 → D + D − Λ B B 0 → D + D − K S 0 = 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) B B 0 → D + D − K S 0 , and the cross-section ratio, σΛb⁰/σB⁰ σ Λ b 0 / σ B 0 , previously measured by LHCb are used to derive the branching fraction of the Λb⁰ Λ b 0 → D + D − Λ decay B(Λb⁰→ D⁺D⁻Λ )=(1.24± 0.15± 0.10± 0.28± 0.11)× 10⁻⁴, B Λ b 0 → 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) B B 0 → D + D − K S 0 and σΛb⁰/σB⁰ σ Λ b 0 / σ B 0 , respectively. Inspection of the D + Λ and D + D − invariant-mass distributions suggests a rich presence of intermediate resonances in the decay. The Λb⁰ Λ b 0 → D *+ D − Λ decay is also observed for the first time as a partially reconstructed component in the D + D − Λ invariant mass spectrum.