Collinear factorization with non-zero quark virtuality in a spectator model

In perturbative QCD, the masses of the hadrons involved in high energy reactions can usually be neglected. However, in the case of production of Kaons in electron-proton collisions at low (and not so low) beam energies this may not be a good approximation. In particular, a recent proposal to include hadron masses in theoretical calculations shows how these Hadron Mass Corrections can explain a large discrepancy observed in measurements performed at the HERMES and COMPASS experiments. In this talk, I will present some preliminary spectator model calculations designed to test the range of validity of the approximations needed in the proposed factorization scheme.