Polarized inclusive leptoproduction, lN->hX, and the hadron helicity density matrix p(h): Possible measurements and predictions

We discuss the production of hadrons in polarized lepton-nucleon interactions and in the current jet fragmentation region; using the QCD hard scattering formalism we compute the helicity density matrix of the: hadron and show how its elements, when measurable, can give information on the spill structure of the nucleon and the spin dependence of the quark fragmentation process. The cases of rho vector mesons and Lambda baryons are considered in more detail and, within simplifying assumptions, some estimates are given.