  We study polarized Semi-Inclusive Deep Inelastic Scattering (SIDIS)
processes, within the QCD parton model and a factorization scheme, taking into
account all transverse motions, of partons inside the initial proton and of
hadrons inside the fragmenting partons. We use the helicity formalism. The
elementary interactions are computed at LO with non collinear exact kinematics,
which introduces phases in the expressions of their helicity amplitudes.
Several Transverse Momentum Dependent (TMD) distribution and fragmentation
functions appear and contribute to the cross sections and to spin asymmetries.
Our results agree with those obtained with different formalisms, showing the
consistency of our approach. The full expression for single and double spin
asymmetries is derived. Simplified, explicit analytical expressions, convenient
for phenomenological studies, are obtained assuming a factorized Gaussian
dependence on intrinsic momenta for the TMDs.
