Structure of the nucleon's low-lying excitations

Understand

A continuum approach to the three valence-quark bound-state problem in quantum field theory is used to perform a comparative study of the four lightest $(I=1/2,J^P = 1/2^\pm)$ baryon isospin-doublets in order to elucidate their structural similarities and differences.

• Such analyses predict the presence of nonpointlike, electromagnetically-active quark-quark (diquark) correlations within all baryons; and in these doublets, isoscalar-scalar, isovector-pseudovector, isoscalar-pseudoscalar, and vector diquarks can all play a role.
• In the two lightest $(1/2,1/2^+)$ doublets, however, scalar and pseudovector diquarks are overwhelmingly dominant.
• The associated rest-frame wave functions are largely $S$-wave in nature; and the first excited state in this $1/2^+$ channel has the appearance of a radial excitation of the ground state.