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Remarks on measurement of the decay $Ξ_b^- \to Λ_b π^-$

The interpretation of the recent observation by LHCb of a heavy-flavor-conserving and strangeness-changing decay $Ξ_b^- \to Λ_b π^-$ in terms of the branching fraction for the decay suffers from the uncertainty in the yield of the $Ξ_b^-$ hyperons relative to that of the $Λ_b$. It is pointed out here that this relative yield can be determined with a significantly reduced uncertainty by measuring within the same experimental conditions the decays related by the flavor $SU(3)$ symmetry and/or the heavy quark symmetry, such as $Ξ_b \to J/ψ\, Ξ$, $Λ_b \to J/ψ\, Λ$, or $Ξ_b^- \to Ξ_c^0 \ell ν$, $Λ_b \to Λ_c \ell ν$.