A narrow structure in the $p\overline{\mathrm{\Lambda }}$ system near the mass threshold, named as $X(2085)$, is observed in the process $e^{+}{e}^{-}\to p{K}^{-}\overline{\mathrm{\Lambda }}$ 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 a statistical significance greater than $5\sigma$ over other quantum numbers ($0^{-},1^{-}$ and $2^{+}$). The pole positions of $X(2085)$ are measured to be $M_{\mathrm{pole}}=(2084_{-2}^{+4}\pm 9)\mathrm{MeV}$ and ${\mathrm{\Gamma }}_{\mathrm{pole}}=(58_{-3}^{+4}\pm 25)\mathrm{MeV}$, where the first uncertainties are statistical and the second ones are systematic. The analysis is based on the study of the process $e^{+}{e}^{-}\to p{K}^{-}\overline{\mathrm{\Lambda }}$ 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 $8.35{\mathrm{fb}}^{-1}$.

• Received 6 March 2023
• Revised 22 August 2023
• Accepted 15 September 2023

DOI:https://doi.org/10.1103/PhysRevLett.131.151901

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Published by the American Physical Society