Single-spin asymmetries have been measured for semi-inclusive electroproduction of $\pi^+$, $\pi^-$, $\pi^0$ and $K^+$ mesons in deep-inelastic scattering off a longitudinally polarised deuterium target. The asymmetries appear in the distribution of the hadrons in the azimuthal angle $\phi$ around the virtual photon direction, relative to the lepton scattering plane. The corresponding analysing powers in the $\sin \phi$ moment of the cross section are $0.012 \pm 0.002 { (stat.)} \pm 0.002 { (syst.)}$ for $\pi^+$, $0.006 \pm 0.003 { (stat.)} \pm 0.002 { (syst.)}$ for $\pi^-$, $0.021 \pm 0.005 { (stat.)} \pm 0.003 { (syst.)}$ for $\pi^0$ and $0.013 \pm 0.006 { (stat.)} \pm 0.003 { (syst.)}$ for $K^+$. The $\sin 2\phi$ moments are compatible with zero for all particles.
Categories: hep-ex