The considerable polarization of hyperons produced at high $x_F$ has been known for a long time and has been interpreted with various theoretical models in terms of the constituents' spin. Recently, the analyzing power in inclusive ${\Lambda }^0$ hyperon production has also been measured using the $200\mathrm{GeV}/c$ Fermilab polarized proton beam. The covered kinematic range is $0.2\le x_F\le 1.0$ and $0.1\le p_T\le 1.5\mathrm{GeV}/c$. The data indicate a negative asymmetry at large $x_F$ and moderate $p_T$. These results can further test the current ideas on the underlying mechanisms for hyperon polarization.

• Received 5 December 1994

DOI:https://doi.org/10.1103/PhysRevLett.75.3073