Electromagnetic excitations in the constituent quark model

Abstract

The description of the electromagnetic properties of baryons with explicit reference to the quark degrees of freedom is reviewed. After a short discussion of the available phenomenological information, such as magnetic moments, form factors and photnexcitation amplitudes, the constituent quark model in the potential approach is introduced and the consequent description of the baryon spectrum is briefly discussed. The model is then systematically used as a theoretical framework for the interpretation of the experimental baryon data, including photon-proton scattering and pion photoproduction, and for the discussion of recent studies of the electromagnetic properties of few-nucleon systems. In particular, the reformulation of meson exchange currents in terms of quark degrees of freedom is reported and the results of various quark approaches to the form factors are presented. Finally, some recent improvements and future developments are briefly discussed.

Helicity-dependent generalized parton distributions and composite constituent quarks

“…Such a ff reproduces well the data at the low values of ∆ 2 which are accessible in the present approach. For higher values of ∆ 2 , it would not be realistic [51]. The same quality of results is expected for the proton axial form factor, which is obtained by integrating Eq.…”

Generalized parton distributions and composite constituent quarks

“…Such a form factor reproduces well the data at the low values of ∆ 2 which are accessible in the present approach. For higher values of ∆ 2 , it would not be realistic [51].…”

Photocouplings of nucleon resonances with gluon and pion exchange currents

“…[26]. Column G is an almost equivalent configuration mixing obtained within the same model [41] but with a different choice of the parameters. Column WW is the corrected result of ref.…”