  Global polarization of $\Xi$ and $\Omega$ hyperons has been measured for the
first time in Au+Au collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV. The
measurements of the $\Xi^-$ and $\bar{\Xi}^+$ hyperon polarization have been
performed by two independent methods, via analysis of the angular distribution
of the daughter particles in the parity violating weak decay
$\Xi\rightarrow\Lambda+\pi$, as well as by measuring the polarization of the
daughter $\Lambda$-hyperon, polarized via polarization transfer from its
parent. The polarization, obtained by combining the results from the two
methods and averaged over $\Xi^-$ and $\bar{\Xi}^+$, is measured to be $\langle
P_\Xi \rangle = 0.47\pm0.10~({\rm stat.})\pm0.23~({\rm syst.})\,\%$ for the
collision centrality 20\%-80\%. The $\langle P_\Xi \rangle$ is found to be
slightly larger than the inclusive $\Lambda$ polarization and in reasonable
agreement with a multi-phase transport model (AMPT). The $\langle P_\Xi
\rangle$ is found to follow the centrality dependence of the vorticity
predicted in the model, increasing toward more peripheral collisions. The
global polarization of $\Omega$, $\langle P_\Omega \rangle = 1.11\pm0.87~({\rm
stat.})\pm1.97~({\rm syst.})\,\%$ was obtained by measuring the polarization of
daughter $\Lambda$ in the decay $\Omega \rightarrow \Lambda + K$, assuming the
polarization transfer factor $C_{\Omega\Lambda}=1$.
