Spin effects in the fragmentation of a transversely polarized quark

An azimuthal dependence of pions produced in polarized Deep Inelastic Scattering, gamma^* - p(transv. polarized) -> pion + X, has been recently observed and might be related to the so-called Collins effect. We discuss in details, for a general spin configuration of the nucleon, the kinematics of the process and methods of extracting information on the fragmentation properties of a polarized quark. Assuming that the observed azimuthal dependence is indeed due to Collins effect, we derive a lower bound estimate for the size of the quark analysing power, which turns out to be large.