Observation of the Decay ${\mathrm{\Xi }}_b^{-}\to p{K}^{-}{K}^{-}$

Decays of the ${\mathrm{\Xi }}_b^{-}$ and ${\mathrm{\Omega }}_b^{-}$ baryons to the charmless final states $p{h}^{-}{h}^{\prime -}$, where $h^{(\prime )}$ denotes a kaon or pion, are searched for with the LHCb detector. The analysis is based on a sample of proton-proton collision data collected at center-of-mass energies $\sqrt{s}=7$ and 8 TeV, corresponding to an integrated luminosity of $3{\mathrm{fb}}^{-1}$. The decay ${\mathrm{\Xi }}_b^{-}\to p{K}^{-}{K}^{-}$ is observed with a significance of 8.7 standard deviations, and evidence at the level of 3.4 standard deviations is found for the ${\mathrm{\Xi }}_b^{-}\to p{K}^{-}{\pi }^{-}$ decay. Results are reported, relative to the $B^{-}\to K^{+}{K}^{-}{K}^{-}$ normalization channel, for the products of branching fractions and $b$-hadron production fractions. The branching fractions of ${\mathrm{\Xi }}_b^{-}\to p{K}^{-}{\pi }^{-}$ and ${\mathrm{\Xi }}_b^{-}\to p{\pi }^{-}{\pi }^{-}$ relative to ${\mathrm{\Xi }}_b^{-}\to p{K}^{-}{K}^{-}$ decays are also measured.

Figure 1

Tree (left) and loop (right) diagrams for the ${\mathrm{\Xi }}_b^{-}\to p{K}^{-}{K}^{-}$ decay channel.

Figure 2

Mass distributions for $b$-hadron candidates in the (top left) $p{K}^{-}{K}^{-}$, (top right) $p{K}^{-}{\pi }^{-}$, (bottom left) $p{\pi }^{-}{\pi }^{-}$, and (bottom right) $K^{+}{K}^{-}{K}^{-}$ final states. Results of the fits are shown with dark blue solid lines. Signals for ${\mathrm{\Xi }}_b^{-}$ and $B^{-}({\mathrm{\Omega }}_b^{-})$ decays are shown with pink (light green) dashed lines, combinatorial backgrounds are shown with gray long-dashed lines, cross-feed backgrounds are shown with red dot-dashed lines, and partially reconstructed backgrounds are shown with dark blue double-dot-dashed lines.

Figure 3

Efficiency-corrected and background-subtracted [36] $m(p{K}^{-}{)}_{\min }$ distribution from ${\mathrm{\Xi }}_b^{-}\to p{K}^{-}{K}^{-}$ candidates.