Helicity Amplitudes In the Hypercentral Constituent Quark Model

Abstract

We report on the recent results of the hypercentral constituent quark model. The model contains a spin independent three-quark interaction which is inspired by QCD lattice calculations and reproduces the average energy values of the SU(6) multiplets. The splittings are obtained with a residual generalized SU(6)-breaking interaction, including an isospin dependent term. The long standing problem of the Roper resonance is absent and all the 3- and 4-star states are well reproduced. The model has also been used for predictions concerning the electromagnetic transition form factors giving a good description of the medium $Q^2$ -behaviour. In particular the calculated $S_{11} A_{{1/2}}$ helicity amplitude agrees very well with the recent CLAS data. Finally the ratio of the elastic form factors of the proton, calculated including kinematic relativistic corrections, exhibits a substantial decreasing with $Q^2$ in agreement with the recent TJNAF experiment.