Study of excited $\mathrm{\Xi }$ states in $\psi (3686)\to K^{-}\mathrm{\Lambda }{\bar{\mathrm{\Xi }}}^{+}+c\mathrm{.}c\mathrm{.}$

Based on a sample of $(448.1\pm 2.9)\times {10}^6$ $\psi (3686)$ events collected with the BESIII detector at BEPCII, the decays of $\psi (3686)\to K^{-}\mathrm{\Lambda }{\bar{\mathrm{\Xi }}}^{+}+c\mathrm{.}c\mathrm{.}$ with ${\bar{\mathrm{\Xi }}}^{+}\to \bar{\mathrm{\Lambda }}{\pi }^{+}$, $\bar{\mathrm{\Lambda }}\to \bar{p}{\pi }^{+}$ are studied.Two excited hyperons, $\mathrm{\Xi }(1690{)}^{-}$ and $\mathrm{\Xi }(1820{)}^{-}$, are observed with large significance ($\gg 10\sigma$) in the $K^{-}\mathrm{\Lambda }$ invariant mass distributions. A partial wave analysis is performed, and the spin-parities of $\mathrm{\Xi }(1690{)}^{-}$ and $\mathrm{\Xi }(1820{)}^{-}$ are determined to be ${\frac{1}{2}}^{-}$ and ${\frac{3}{2}}^{-}$, respectively. The masses, widths, and product branching fractions of $\mathrm{\Xi }(1690{)}^{-}$ and $\mathrm{\Xi }(1820{)}^{-}$ are also measured.