Spin effects in the fragmentation of a transversely polarized quark

An azimuthal dependence of pions produced in polarized Deep inelastic Scatt ering, gamma(*)p(up arrow) --> pi X, has been recently observed and might b e related to the so-called Collins effect. We discuss in details, for a gen eral spin configuration of the nucleon, the kinematics of the process and m ethods of extracting information on the fragmentation properties of a polar ized quark. Assuming that the observed azimuthal dependence is indeed due t o Collins effect, we derive a lower bound estimate for the size of the quar k analysing power, which turns out to be large. (C) 2000 Elsevier Science B .V. All rights reserved.