General tensor structure for electron scattering in terms of invariant responses

Abstract

The use of invariant response functions in treatments of electron scattering from hadronic targets is reviewed. Various classes of reaction are treated, building from the simplest (and best known) case of inclusive scattering from unpolarized targets, to more complicated cases involving polarized electrons and possibly polarized spin-1/2 targets. In particular, the general structure of semi-inclusive polarized electron scattering from polarized spin-1/2 targets is emphasized. A summary is presented of how the leptonic and hadronic tensors that enter in the formalism are constructed in a general covariant way in terms of kinematic factors that are frame dependent but model independent and invariant response functions which contain all of the model-dependent dynamics. In the process of reviewing the general problem the relationships to the conventional responses expressed in terms of the frame-dependent helicity components of the exchanged virtual photon are presented.