Study of the $B^0 \to \Lambda_c^+ \bar{\Lambda}_c^- K_S^0$ decay

The decay $B^0 \to \Lambda_c^+ \bar{\Lambda}_c^- K_S^0$ is studied at LHCb for the first time using proton-proton collision data recorded by the LHCb experiment at a center-of-mass energy of $\sqrt{s} = 13$ TeV, corresponding to an integrated luminosity of 5.4 fb$^{-1}$. The branching ratio relative to the decay $B^+ \to \Lambda_c^+ \bar{\Lambda}_c^- K^+$ is measured to be $$\frac{{\cal B}(B^0 \to \Lambda_c^+ \bar{\Lambda}_c^- K_S^0)}{{\cal B}(B^+ \to \Lambda_c^+ \bar{\Lambda}_c^- K^+)} = 0.53 \pm 0.05 \pm 0.05,$$ where the first uncertainty is statistical and the second is systematic. Evidence is found for contributions from two resonant states, $\Xi_c(2923)^+$ and $\Xi_c(2939)^+$, in the $\Lambda_c^+ K_S^0$ system. The two states show a significance of $3.9\sigma$ relative to the nonresonant hypothesis. These two $\Xi_c^+$ states are consistent with being the isospin partners of the states observed in $\Lambda_c^+ K^-$ system.