  The nuclear response to longitudinally polarized electrons, detected in
coincidence with out-of-plane high-energy protons, is discussed in a simple
model where the ejectile wave function is approximated as a plane wave with a
complex wave vector. This choice is equivalent to solve the problem of
Final-State Interactions (FSI) in homogeneous nuclear matter, as the residual
nucleus can be described to a first approximation when dealing with very fast
emitted protons. The main advantage of the present method is that in the
framework of the Distorted-Wave Impulse Approximation (DWIA) it allows for an
analytical derivation of all the components of the nuclear response. It emerges
that cancellations among the leading contributions determine the very small
absolute size of the socalled fifth structure function and produce a nontrivial
asymptotic scaling of the related helicity asymmetry for large values of the
momentum transfer.
