Hadronization in polarized semi-inclusive DIS: the question of independent fragmentation

A new formalism for the description of (un)polarized semi-inclusive deep inelastic scattering (DIS) at moderate energies is developed. Hadron production is modeled as a product of distribution functions and hadronization functions (HFs) weighted by the hard scattering cross sections, as has been done in the LEPTO event generator. The correct treatment of polarization effects shows that the description of semi-inclusive DIS (SIDIS) within this formalism includes a new non-perturbative input: polarized HFs. It is shown that this approach does not correspond to that commonly adopted with the independent quark fragmentation. The purity method used by the HERMES collaboration mixes the two approaches and ignores the contributions from polarized HFs. This method cannot be considered a precise tool for the extraction of polarized quark distributions from measured SIDIS asymmetries.