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 $\Xi_b^- \to \Lambda_b \pi^-$ in terms of the branching fraction for the decay suffers from the uncertainty in the yield of the $\Xi_b^-$ hyperons relative to that of the $\Lambda_b$. 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 $\Xi_b \to J/\psi \, \Xi$, $\Lambda_b \to J/\psi \, \Lambda$, or $\Xi_b^- \to \Xi_c^0 \ell \nu$, $\Lambda_b \to \Lambda_c \ell \nu$.