First observation of the $\mathit{\Lambda}_b^{0}\!\rightarrow\mathit{\Lambda}_{c}^{+}D_{s}^{-}K^{+}K^{-}$ decay and search for pentaquarks in the $\mathit{\Lambda}_{c}^{+}D_{s}^{-}$ system

Abstract

The $\mathit{\Lambda}_b^{0}\!\rightarrow\mathit{\Lambda}_{c}^{+}D_{s}^{-}K^{+}K^{-}$ decay is observed for the first time using the data sample from proton-proton collisions recorded at a center-of-mass energy of $13\,\text{TeV}$ with the LHCb detector, corresponding to an integrated luminosity of $6\,\text{fb}^{-1}$. The ratio of branching fraction to that of $\mathit{\Lambda}_b^{0} \!\rightarrow\mathit{\Lambda}_{c}^{+}D_{s}^{-}$ decays is measured as $0.0141 \pm 0.0019 \pm 0.0012$, where the first uncertainty is statistical and the second systematic. A search for hidden-charm pentaquarks with strangeness is performed in the $\mathit{\Lambda}_{c}^{+}D_{s}^{-}$ system. No evidence is found, and upper limits on the production ratio of $P_{c\bar{c}s}(4338)^0$ and $P_{c\bar{c}s}(4459)^0$ pentaquarks relative to the $\mathit{\Lambda}_{c}^{+}D_{s}^{-}$ final state are set at the $95\%$ confidence level as $0.12$ and $0.20$, respectively.