Observation of the Λ b 0 → J / ψ Ξ - K + decay

Abstract

Using proton-proton collision data corresponding to an integrated luminosity of $140{\text{fb}}^{-1}$ collected by the CMS experiment at $\sqrt{s}=13\text{Te}\text{V}$ , the ${\Lambda }_{\text{b}}^0\to \text{J}/\psi {\Xi }^{-}{\text{K}}^{+}$ decay is observed for the first time, with a statistical significance exceeding 5 standard deviations. The relative branching fraction, with respect to the ${\Lambda }_{\text{b}}^0\to \psi \left(2\text{S}\right)\Lambda$ decay, is measured to be $B({\Lambda }_{\text{b}}^0\to \text{J}/\psi {\Xi }^{-}{\text{K}}^{+})/B({\Lambda }_{\text{b}}^0\to \psi \left(2\text{S}\right)\Lambda )=[3.38\pm 1.02\pm 0.61\pm 0.03]\%$ , where the first uncertainty is statistical, the second is systematic, and the third is related to the uncertainties in $B(\psi \left(2\text{S}\right)\to \text{J}/\psi {\pi }^{+}{\pi }^{-})$ and $B({\Xi }^{-}\to \Lambda {\pi }^{-})$ .