Longitudinal polarization of $\Lambda$ and anti-$\Lambda$ in DIS at COMPASS

The longitudinal polarization transfer from polarized muons to$\Lambda$ and $\bar{\Lambda}$ hyperons has been studied in deep-inelastic scattering at the COMPASS experiment at CERN. The average longitudinal spin transfer to $\Lambda$ is small: $S_{X}(\Lambda) =-$0.012 $\pm$ 0.047 $\pm$ 0.024 at $\bar{x}_{F} =$ 0.22. The longitudinal spin transfer to $\bar{\Lambda}$ is larger: $S_{X}(\bar{\Lambda})=$ 0.249 $\pm$ 0.056 $\pm$ 0.049 at $\bar{x}_{F}=$ 0.20. The measured $x$ and $x_{F}$ dependences of the longitudinal spin transfer turns out to be different for$\Lambda$ and $\bar{\Lambda}$ hyperons. The $S_{X}(\Lambda)$ is compatible with zero for all $x$, while $S_{X}(\bar{\Lambda})$ increases with $x$ and $x_{F}$ and may become as large as $S_{X}(\bar{\Lambda}) =$ 0.4 $-$ 0.5.