Quark model predictions for the SU(6)-breaking ratio of the proton momentum distributions

The ratio between the anomalous magnetic moments of proton and neutron has recently been suggested to be connected to the ratio of proton momentum fractions carried by valence quarks. This ratio is evaluated using different constituent quark models, starting from the CQM density distributions and calculating the next-to-leading order distributions. We show that this momentum fraction ratio is a sensitive test for SU(6)-breaking effects and is a useful observable to distinguish among different CQMs. We investigate also the possibility of getting constraints on the formulation of quark structure models.