Observation of $${{\varxi } ^0_{b}} \rightarrow {{\varxi } ^+_{c}} {{D} ^-_{S}} $$ and $${{\varxi } ^-_{B}} \rightarrow {{\varxi } ^0_{c}} {{D} ^-_{S}} $$ Decays

The $$\Xi _b^0 \rightarrow \Xi _c^+ D_s^-$$ Ξ b 0 → Ξ c + D s - and $$\Xi _b^- \rightarrow \Xi _c^0 D_s^-$$ Ξ b - → Ξ c 0 D s - decays are observed for the first time using proton-proton collision data collected by the LHCb experiment at a centre-of-mass energy of $$\sqrt{s}=13\,\,\textrm{TeV}$$ s = 13 TeV , corresponding to an integrated luminosity of $$5.1\,\,\textrm{fb}^{-1}$$ 5.1 fb - 1 . The branching fractions times the production cross-sections of $$\Xi _b$$ Ξ b baryons relative to that of $$\Lambda _b^0$$ Λ b 0 baryon are measured to be $$\begin{aligned} \mathcal {R}\left( \frac{\Xi _b^0}{\Lambda _b^0}\right)&\equiv \frac{\sigma \left( \Xi _b^0\right) }{\sigma \left( \Lambda _b^0\right) } \times \frac{\mathcal {B}\left( \Xi _b^0 \rightarrow \Xi _c^+ D_s^-\right) }{\mathcal {B}\left( \Lambda _b^0 \rightarrow \Lambda _c^0 D_s^-\right) }\\&=(15.8\pm 1.1\pm 0.6\pm 7.7)\%,\\ \mathcal {R}\left( \frac{\Xi _b^-}{\Lambda _b^0}\right)&\equiv \frac{\sigma \left( \Xi _b^-\right) }{\sigma \left( \Lambda _b^0\right) } \times \frac{\mathcal {B}\left( \Xi _b^- \rightarrow \Xi _c^0 D_s^-\right) }{\mathcal {B}\left( \Lambda _b^0 \rightarrow \Lambda _c^0 D_s^-\right) } \\&=(16.9\pm 1.3\pm 0.9\pm 4.3)\%, \end{aligned}$$ R Ξ b 0 Λ b 0 ≡ σ Ξ b 0 σ Λ b 0 × B Ξ b 0 → Ξ c + D s - B Λ b 0 → Λ c 0 D s - = ( 15.8 ± 1.1 ± 0.6 ± 7.7 ) % , R Ξ b - Λ b 0 ≡ σ Ξ b - σ Λ b 0 × B Ξ b - → Ξ c 0 D s - B Λ b 0 → Λ c 0 D s - = ( 16.9 ± 1.3 ± 0.9 ± 4.3 ) % , where the first uncertainties are statistical, the second systematic, and the third due to the uncertainties on the decay branching fractions of relevant charmed baryons. The masses of $$\Xi _b^0$$ Ξ b 0 and $$\Xi _b^-$$ Ξ b - baryons are measured to be $$m_{\Xi _b^0}=5791.12\pm 0.60\pm 0.45\pm 0.24\,\,\textrm{MeV}/c^2$$ m Ξ b 0 = 5791.12 ± 0.60 ± 0.45 ± 0.24 MeV / c 2 and $$m_{\Xi _b^-}=5797.02\pm 0.63\pm 0.49\pm 0.29\,\,\textrm{MeV}/c^2$$ m Ξ b - = 5797.02 ± 0.63 ± 0.49 ± 0.29 MeV / c 2 , where the uncertainties are statistical, systematic, and those due to charmed-hadron masses, respectively.