Single-spin azimuthal asymmetries in electroproduction of neutral pions in semi-inclusive deep-inelastic scattering

A single-spin asymmetry in the azimuthal distribution of neutral pions relative to the lepton scattering plane has been measured for the first time in deep-inelastic scattering of positrons off longitudinally polarized protons. The analyzing power in the $\mathrm{sin}\ensuremath{\varphi}$ moment of the cross section is $0.019\ifmmode\pm\else\textpm\fi{}0.007(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.003(\mathrm{syst}).$ This result is compared to single-spin asymmetries for charged pion production measured in the same kinematic range. The ${\ensuremath{\pi}}^{0}$ asymmetry is of the same size as the ${\ensuremath{\pi}}^{+}$ asymmetry and shows a similar dependence on the relevant kinematic variables. The asymmetry is described by a phenomenological calculation based on a fragmentation function that represents sensitivity to the transverse polarization of the struck quark.