Study of the $B^{-}\to {\mathrm{\Lambda }}_c^{+}{\bar{\mathrm{\Lambda }}}_c^{-}{K}^{-}$ decay

The decay $B^{-}\to {\mathrm{\Lambda }}_c^{+}{\bar{\mathrm{\Lambda }}}_c^{-}{K}^{-}$ is studied in proton-proton collisions at a center-of-mass energy of $\sqrt{s}=13$ TeV using data corresponding to an integrated luminosity of 5 ${\mathrm{f}\mathrm{b}}^{-1}$ collected by the LHCb experiment. In the ${\mathrm{\Lambda }}_c^{+}{K}^{-}$ system, the ${\mathrm{\Xi }}_c(2930{)}^0$ state observed at the BaBar and Belle experiments is resolved into two narrower states, ${\mathrm{\Xi }}_c(2923{)}^0$ and ${\mathrm{\Xi }}_c(2939{)}^0$, whose masses and widths are measured to be $$m({\mathrm{\Xi }}_c(2923{)}^0)=2924.5\pm 0.4\pm 1.1\mathrm{M}\mathrm{e}\mathrm{V},m({\mathrm{\Xi }}_c(2939{)}^0)=2938.5\pm 0.9\pm 2.3\mathrm{M}\mathrm{e}\mathrm{V},\mathrm{\Gamma }({\mathrm{\Xi }}_c(2923{)}^0)=\phantom{000}4.8\pm 0.9\pm 1.5\mathrm{M}\mathrm{e}\mathrm{V},\mathrm{\Gamma }({\mathrm{\Xi }}_c(2939{)}^0)=\phantom{00}11.0\pm 1.9\pm 7.5\mathrm{M}\mathrm{e}\mathrm{V},$$ where the first uncertainties are statistical and the second systematic. The results are consistent with a previous LHCb measurement using a prompt ${\mathrm{\Lambda }}_c^{+}{K}^{-}$ sample. Evidence of a new ${\mathrm{\Xi }}_c(2880{)}^0$ state is found with a local significance of $3.8\sigma$, whose mass and width are measured to be $2881.8\pm 3.1\pm 8.5\mathrm{M}\mathrm{e}\mathrm{V}$ and $12.4\pm 5.3\pm 5.8\mathrm{M}\mathrm{e}\mathrm{V}$, respectively. In addition, evidence of a new decay mode ${\mathrm{\Xi }}_c(2790{)}^0\to {\mathrm{\Lambda }}_c^{+}{K}^{-}$ is found with a significance of $3.7\sigma$. The relative branching fraction of $B^{-}\to {\mathrm{\Lambda }}_c^{+}{\bar{\mathrm{\Lambda }}}_c^{-}{K}^{-}$ with respect to the $B^{-}\to D^{+}{D}^{-}{K}^{-}$ decay is measured to be $2.36\pm 0.11\pm 0.22\pm 0.25$, where the first uncertainty is statistical, the second systematic and the third originates from the branching fractions of charm hadron decays.