Determination of Spin-parity Quantum Numbers for the Narrow Structure Near the $p\bar{\mathrm{\Lambda }}$ Threshold in $e^{+}{e}^{-}\to p{K}^{-}\bar{\mathrm{\Lambda }}+c\mathrm{.}c\mathrm{.}$

A narrow structure in the $p\bar{\mathrm{\Lambda }}$ system near the mass threshold, named as $X(2085)$, is observed in the process $e^{+}{e}^{-}\to p{K}^{-}\bar{\mathrm{\Lambda }}$ 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 statistical significance greater than $5\sigma$ over other quantum numbers. The pole positions of $X(2085)$ are measured to be $M_{\mathrm{p}\mathrm{o}\mathrm{l}\mathrm{e}}=(2086\pm 4\pm 6)$~MeV and ${\mathrm{\Gamma }}_{\mathrm{p}\mathrm{o}\mathrm{l}\mathrm{e}}=(56\pm 5\pm 16)$ MeV, where the first uncertainties are statistical and the second ones are systematic. The analysis is based on the study of the process $e^{+}{e}^{-}\to p{K}^{-}\bar{\mathrm{\Lambda }}$ 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 $8.35{\text{fb}}^{-1}$.