S-wave nonleptonic hyperon decays and ${\Xi }_b^{-}\to {\pi }^{-}{\Lambda }_b$

Abstract

The decay ${\Xi }_b^{-}\to {\pi }^{-}{\Lambda }_b$ has recently been observed by the LHCb Collaboration at CERN. In contrast to most weak decays of $b$-flavored baryons, this process involves the decay of the strange quark in ${\Xi }_b$, and thus has features in common with nonleptonic weak decays of hyperons. Thanks to the expected pure S-wave nature of the decay in question in the heavy $b$ quark limit, we find that its amplitude may be related to those for S-wave nonleptonic decays of $\Lambda$, $\Sigma$, and $\Xi$ in a picture inspired by duality. The calculated branching fraction $\mathcal{B}({\Xi }_b^{-}\to {\pi }^{-}{\Lambda }_b)=(6.3\pm 4.2)\times 10^{-3}$ is consistent with the range allowed in the LHCb analysis. The error is dominated by an assumed 30\% uncertainty in the amplitude due to possible U(3) violation. A more optimistic view based on sum rules involving nonleptonic hyperon decay S-wave amplitudes reduces the error on the branching fraction to $2.0\times 10^{-3}$.

Comments: 8 pages, 1 figure. Slightly revised version submitted to Phys. Rev. D