Analyzing power of inclusive production of ${\pi }^{+}$, ${\pi }^{-}$, and $K_S^0$ by polarized protons at 13.3 and 18.5 GeV/c

We have measured the analyzing power in ${\pi }^{+}$, ${\pi }^{-}$, and $K_S^0$ production by a polarized proton beam at 13.3 and 18.5 GeV/c. The data cover the central and the beam fragmentation region, in the transverse-momentum range up to 2 GeV/c. The results indicate that sizable effects are present at high $x_F$ and also persist into the hard-scattering region for $K_S^0$ and ${\pi }^{+}$. A zero value of the analyzing power was observed for ${\pi }^{-}$ production.