Observation of the $Λ_\text{b}^0$ $\to$ J/$ψΞ^-$K$^+$ decay

Abstract

Using proton-proton collision data corresponding to an integrated luminosity of 140 fb$^{-1}$ collected by the CMS experiment at $\sqrt{s}$ = 13 TeV, the $Λ_\text{b}^0$ $\to$ J/$ψΞ^-$K$^+$ decay is observed for the first time, with a statistical significance exceeding 5 standard deviations. The relative branching fraction, with respect to the $Λ_\text{b}^0$ $\to$ $ψ$(2S)$Λ$ decay, is measured to be $\mathcal{B}$($Λ_\text{b}^0$ $\to$ J/$ψΞ^-$K$^+$) / $\mathcal{B}$( $Λ_\text{b}^0$ $\to$ $ψ$(2S)$Λ$) = [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 $\mathcal{B}$($ψ$(2S) $\to$ J/$ψπ^+π^-$) and $\mathcal{B}$($Ξ^-$ $\to$ $Λπ^-$).