Nucleon transversity distribution from azimuthal spin asymmetry in pion electroproduction

The azimuthal asymmetry observed by the HERMES Collaboration in semi-inclusive pion production in deep inelastic scattering of an unpolarized positron on a longitudinally polarized proton target can provide information on the quark transversity distributions of the nucleon. We show that the quark transversity distributions predicted by both the light-cone quark-spectator-diquark model and a PQCD inspired model can give consistent descriptions of the available HERMES data for the analyzing powers A_UL^{sin φ} and A_UL^{sin 2φ} for π⁺ and π^- productions. We also show that the two models give similar predictions of A_UL^{sin φ} for π⁺ production, whereas they give very different predictions of A_UL^{sin φ} for π^- production at large x. Further precision measurement of A_UL^{sin φ} for π^- production can provide a decisive test of different models.