Form Factors of Excited Baryons

Abstract

Abstract The finding that the nucleon is an extended object (Hofstadter and McAllister 1955; Chambers and Hofstadter 1956; Hofstadter 1956) with an internal structure (Bloom et al. 1969; Breidenbach et al. 1969; Miller et al. 1972; Friedman and Kendall 1972) immediately calls for an understanding of its excitation spectrum. The excitation spectrum of the nucleon has been extensively studied by pion scattering and a large number of states have been discovered after the pioneering work of Fermi and coworkers (Anderson et al. 1952). Baryon states are classified by the Particle Data Group (Montanet et al. 1994) according to a quark model based on SU(6) spin-flavour symmetry. The structure and dynamics of hadrons have to be understood in terms of a theoretical description of strong interactions ultimately derived from QCD, but in a regime where the underlying QCD dynamics cannot be treated perturbatively. Thus the complexity of hadrons requires the development of soluble models not only retaining the basic symmetries of QCD but at the same time also containing the relevant dynamical features of interacting quarks and gluons. The electromagnetic excitation of nucleon resonances (N*) gives important complementary information on the internal dynamics of baryons since it provides constraints on theoretical models by determining the photocoupling amplitudes associated with the-γNN* vertex at different four-momentum transfers Q2•