Observation of a single spin azimuthal asymmetry in semiinclusive pion electro production

Single-spin asymmetries for semi-inclusive pion production in deep-inelastic scattering have been measured for the first time. A significant target-spin asymmetry of the distribution in the azimuthal angle phi of the pion relative to the lepton scattering plane was observed for pi+ electro-production on a longitudinally polarized hydrogen target. The corresponding analyzing power in the sin(phi) moment of the cross section is 0.022 +/- 0.005 +/- 0.003. This result can be interpreted as the effect of terms in the cross section involving chiral-odd spin distribution functions in combination with a time-reversal-odd fragmentation function that is sensitive to the transverse polarization of the fragmenting quark.

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5 pages of RevTex, 3 ps figures, 2 tables Report-no: DESY 99-149

positron p: deep inelastic scattering
positron p: inclusive reaction
positron: polarized beam
hydrogen: polarized target
polarization: longitudinal
pi+: electroproduction
spin: asymmetry
analyzing power
HERMES
experimental results

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