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

The analyzing power ${A}_{N}$ in inclusive ${\ensuremath{\pi}}^{\ensuremath{-}}$ and ${\ensuremath{\pi}}^{+}$ production has been measured with a 200 GeV/c transversely polarized antiproton beam over a wide ${x}_{F}$ range $(0.2\ensuremath{\le}{x}_{F}\ensuremath{\le}0.9)$ and at moderate ${p}_{T}$ $(0.2\ensuremath{\le}{p}_{T}\ensuremath{\le}1.5\mathrm{GeV}/\mathrm{c})$. The asymmetry ${A}_{N}$ increases with increasing ${x}_{F}$ from zero to large positive values for ${\ensuremath{\pi}}^{\ensuremath{-}}$'s, and decreases from zero to large negative values for ${\ensuremath{\pi}}^{+}$'s. A threshold for the onset of the asymmetry is observed about ${p}_{T}\ensuremath{\sim}0.5\mathrm{GeV}/\mathrm{c}$, below which ${A}_{N}$ is essentially zero and above which ${A}_{N}$ increases (decreases) with ${p}_{T}$ for ${\ensuremath{\pi}}^{\ensuremath{-}}$'s ( ${\ensuremath{\pi}}^{+}$'s) in the covered ${p}_{T}$ range.