Observation and branching fraction measurement of the decay ${\Xi }_b^{-}\to {\Lambda }_b^0{\pi }^{-}$

Abstract

The decay ${\Xi }_b^{-}\to {\Lambda }_b^0{\pi }^{-}$ is observed using a proton-proton collision data sample collected at center-of-mass energy $\sqrt{s}=13$ TeV with the LHCb detector, corresponding to an integrated luminosity of 5.5 fb${}^{-1}$. This process is mediated by the $s\to u\bar{u}d$ quark-level transition, where the $b$ quark in the ${\Xi }_b^{-}$ baryon is a spectator in the decay. Averaging the results obtained using the two ${\Lambda }_b^0$ decay modes, ${\Lambda }_b^0\to {\Lambda }_c^{+}{\pi }^{-}$ and ${\Lambda }_b^0\to {\Lambda }_c^{+}{\pi }^{-}{\pi }^{+}{\pi }^{-}$, the relative production ratio is measured to be $(f_{{\Xi }_b^{-}}/f_{{\Lambda }_b^0})\mathcal{B}({\Xi }_b^{-}\to {\Lambda }_b^0{\pi }^{-})=(7.3\pm 0.8\pm 0.6)\times 10^{-4}$. Here the uncertainties are statistical and systematic, respectively, and $f_{{\Xi }_b^{-}}(f_{{\Lambda }_b^0})$ is the fragmentation fraction for a $b$ quark into a ${\Xi }_b^{-}$ (${\Lambda }_b^0$) baryon. Using an independent measurement of $f_{{\Xi }_b^{-}}/f_{{\Lambda }_b^0}$, the branching fraction $\mathcal{B}({\Xi }_b^{-}\to {\Lambda }_b^0{\pi }^{-})=(0.89\pm 0.10\pm 0.07\pm 0.29)\%$ is obtained, where the last uncertainty is due to the assumed SU(3) flavor symmetry in the determination of $f_{{\Xi }_b^{-}}/f_{{\Lambda }_b^0}$.

14 pages, 4 figures. All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2023-015.html (LHCb public pages)

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