Study of beauty hadron decays into Pairs of charm hadrons

First observations of the decays Λ_b ⁰→ Λ_c ⁺D_(s) ^-are reported using data corresponding to an integrated luminosity of 3fb^-1collected at 7 and 8 TeV center-of-mass energies in proton-proton collisions with the LHCb detector. In addition, the most precise measurement of the branching fraction B(B_s ⁰→D⁺D_s ^-) is made and a search is performed for the decays B_(s) ⁰→Λ_c ⁺Λ_c ^-. The results obtained are B(Λ_b ⁰→Λ_c ⁺D^-)/ B(Λ_b ⁰→Λ_c ⁺D_s ^-)=0.042±0.003(stat)±0.003(syst), [B(Λ_b ⁰→Λ_c ⁺D_s ^-)/B(B̄⁰→D⁺D_s ^-)]/[B(Λ_b ⁰→Λ_c ⁺π^-)/B(B̄⁰→D⁺π^-)]=0.96±0.02(stat)±0.06(syst),B(B_s ⁰→D⁺D_s ^-)/ B(B̄⁰→D⁺D_s ^-)=0. 038±0.004(stat)±0.003(syst),B(B̄⁰→Λ_c ⁺Λ_c ^-)/B(B̄⁰→D⁺D_s ^-)<0.0022[95%C.L.], B(B_s ⁰→Λ_c ⁺Λ_c ^-)/B(B_s ⁰→D⁺D_s ^-)<0.30[95%C.L.]. Measurement of the mass of the Λ_b ⁰baryon relative to the B̄⁰meson gives M(Λ_b ⁰)-M(B̄⁰)=339. 72±0.24(stat)±0.18(syst)MeV/c². This result provides the most precise measurement of the mass of the Λ_b ⁰baryon to date.