First observation of Λ

By analysing $\textit{e}$ $\textit{e}$ annihilation data corresponding to an integrated luminosity of 368$\textit{.}$48 pb collected at the centre-of-mass energies of = 4$\textit{.}$918 and 4$\textit{.}$951 GeV with the BESIII detector, we report the first observation of Λ (2595) and Λ (2625) → with statistical significances of 7.9$\textit{σ}$ and 11.8$\textit{σ}$, respectively. The branching fractions of Λ (2595) and Λ (2625) → are measured to be (59$\textit{.}$5 ± 11$\textit{.}$1 ± 7$\textit{.}$9 )% and (41$\textit{.}$0 ± 5$\textit{.}$2 ± 3$\textit{.}$3 )%, respectively. The absolute branching fraction of Λ (2595) is consistent with the expectation of the mechanism referred to as the $\textit{threshold effect}$, proposed for the strong decays of Λ (2595) within uncertainty.