Spin-transfer observables for $\overline{p}p\to \overline{\Lambda }\Lambda$ have been measured using a transversely polarized frozen-spin target and a beam momentum of $1.637\mathrm{G}\mathrm{e}\mathrm{V}\mathrm{/}\mathit{c}$. Current models of the reaction near threshold are in good agreement with existing measurements performed with unpolarized particles in the initial state but produce conflicting predictions for the spin-transfer observables $D_{nn}$ and $K_{nn}$ (the normal-to-normal depolarization and polarization transfer), which are measurable only with polarized target or beam. Measurements of $D_{nn}$ and $K_{nn}$ presented here are found to be in disagreement with predictions from these models.

• Received 2 June 2002

DOI:https://doi.org/10.1103/PhysRevLett.89.212302