Measurement of the polarization and magnetic moment of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mover><mml:mrow><mml:mi>Ξ</mml:mi></mml:mrow><mml:mrow><mml:mi>¯</mml:mi></mml:mrow></mml:mover><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math>antihyperons produced by 800-GeV/<i>c</i>protons

The polarization of ${\overline{\ensuremath{\Xi}}}^{+}$ hyperons produced by 800-GeV/c protons in the inclusive reaction $p+\mathrm{Be}\ensuremath{\rightarrow}{\overline{\ensuremath{\Xi}}}^{+}+X$ has been measured using a sample of $70000{\overline{\ensuremath{\Xi}}}^{+}$ decays. The average polarization of the ${\overline{\ensuremath{\Xi}}}^{+}$, at a mean ${x}_{F}=0.39$ and ${p}_{t}=0.76$ GeV/c, is -0.097\ifmmode\pm\else\textpm\fi{}0.012\ifmmode\pm\else\textpm\fi{}0.009, compared to -0.102\ifmmode\pm\else\textpm\fi{}0.012\ifmmode\pm\else\textpm\fi{}0.010 for the ${\ensuremath{\Xi}}^{\ensuremath{-}}$. The large polarization found for the ${\overline{\ensuremath{\Xi}}}^{+}$ is not expected in any model for polarization of inclusively produced hyperons. The magnetic moment of the ${\overline{\ensuremath{\Xi}}}^{+}$ was measured to be 0.657\ifmmode\pm\else\textpm\fi{}0.028\ifmmode\pm\else\textpm\fi{}0.020 nuclear magnetons (${\ensuremath{\mu}}_{N}$), compared to $(\ensuremath{-}0.674\ifmmode\pm\else\textpm\fi{}0.021\ifmmode\pm\else\textpm\fi{}0.020){\ensuremath{\mu}}_{N}$ for the ${\ensuremath{\Xi}}^{\ensuremath{-}}$, in good agreement with $\mathrm{CPT}$ invariance.