Single-Spin Asymmetries in Inclusive Charged Pion Production by Transversely Polarized Antiprotons

The analyzing power $A_N$ in inclusive ${\pi }^{-}$ and ${\pi }^{+}$ production has been measured with a 200 GeV/c transversely polarized antiproton beam over a wide $x_F$ range $\left(0.2\le x_F\le 0.9\right)$ and at moderate $p_T$ $(0.2\le p_T\le 1.5\mathrm{GeV}/\mathrm{c})$. The asymmetry $A_N$ increases with increasing $x_F$ from zero to large positive values for ${\pi }^{-}$'s, and decreases from zero to large negative values for ${\pi }^{+}$'s. A threshold for the onset of the asymmetry is observed about $p_T\sim 0.5\mathrm{GeV}/\mathrm{c}$, below which $A_N$ is essentially zero and above which $A_N$ increases (decreases) with $p_T$ for ${\pi }^{-}$'s ( ${\pi }^{+}$'s) in the covered $p_T$ range.