Probing transverse quark polarization in deep-inelastic leptoproduction

The azimuthal dependence of hadrons produced in lepton scattering off a polarized hadron probes the quark transverse-spin distributions. In the calculation of the asymmetries, transverse momenta of quarks in the distribution and fragmentation functions must be incorporated. In addition to the $\sin (\varphi +{\varphi }_S)$ asymmetry for transversely polarized hadrons, known as the Collins effect, we find $\sin 2\varphi$ asymmetries for both transversely and longitudinally polarized hadrons.