Determination of Spin-Parity Quantum Numbers for the Narrow Structure near the $p\overline{\Lambda }$ Threshold in ${e}^{+}{e}^{-}\to p{K}^{-}\overline{\Lambda }+c.c.$

A narrow structure in the $p\overline{\Lambda }$ system near the mass threshold, named as $X\left(2085\right)$, is observed in the process ${e}^{+}{e}^{-}\to p{K}^{-}\overline{\Lambda }$ with a statistical significance greater than $20\sigma $. Its spin and parity are determined for the first time to be ${J}^{P}={1}^{+}$ in an amplitude analysis, with a statistical significance greater than $5\sigma $ over other quantum numbers (${0}^{-},{1}^{-}$ and ${2}^{+}$). The pole positions of $X\left(2085\right)$ are measured to be ${M}_{\mathrm{pole}}=\left(208{4}_{-2}^{+4}±9\right)\text{}\text{}\mathrm{MeV}$ and ${\Gamma }_{\mathrm{pole}}=\left(5{8}_{-3}^{+4}±25\right)\text{}\text{}\mathrm{MeV}$, where the first uncertainties are statistical and the second ones are systematic. The analysis is based on the study of the process ${e}^{+}{e}^{-}\to p{K}^{-}\overline{\Lambda }$ and uses the data samples collected with the BESIII detector at the center-of-mass energies $\sqrt{s}=4.008$, 4.178, 4.226, 4.258, 4.416, and 4.682 GeV with a total integrated luminosity of $8.35\text{}\text{}{\mathrm{fb}}^{-1}$.