Electromagnetic form factors in the hypercentral CQM
Universit a di Genova e INFN, Sezione di Genova, via Dodecaneso 33, 16142 Genova, Italy
2 INFN,Sezione di Roma1, Piazzale Aldo Moro, Roma, Italy
Published online: 12 February 2004
We report on the recent results of the hypercentral Constituent Quark Model (hCQM). The model contains a spin independent three-quark interaction which is inspired by Lattice QCD calculations and reproduces the average energy values of the SU(6) multiplets. The splittings are obtained with a SU(6)-breaking interaction, which can include also an isospin dependent term. Concerning Constituent Quark models, we have shown for the first time that the decreasing of the ratio of the elastic form factors of the proton is due to relativistic effects using relativistic corrections to the e.m. current and boosts. Now the elastic nucleon form factors have been recalculated, using a relativistic version of the hCQM and a relativistic quark current showing a very detailed reproduction of all the four form factor existing data over the complete range of 0-4 GeV 2. Futhermore, the model has been used for predictions concerning the electromagnetic transverse and longitudinal transition form factors giving a good description of the medium Q 2 behaviour. We show that the discrepancies in the reproduction of the helicity amplitudes at low Q 2 are due to pion loops. We have calculated the helicity amplitudes for all the 3 and 4 star resonances opening the possibility of application to the evaluation of cross sections.
PACS: codes. – 13.40.Gp - Electromagnetic form factors / codes. – 12.39.Jh - Nonrelativistic quark model / codes. – 14.20.Gk - Baryon resonances and helicity amplitudes / codes. – 12.39.Ki - Relativistic quark model / codes. – 12.39.Pn - Potential Models / codes. – 13.40.Gp - Electromagnetic Form Factors / codes. – 14.30.Gk - Baryon Resonances with S=0 / codes. – 25.20.Lj - Photoproduction reactions / codes. – 25.30.Rw - Electroproduction reactions
© Società Italiana di Fisica, Springer-Verlag, 2004