Structure of the nucleon’s low-lying excitations

Journal Article · 15 February 2018 · Physical Review D

DOI: https://doi.org/10.1103/PhysRevD.97.034016 · OSTI ID:1480433

Chen, Chen ^[1]; El-Bennich, Bruno ^[2]; Roberts, Craig D. ^[3]; Schmidt, Sebastian M. ^[4]; Segovia, Jorge ^[5]; Wan, Shaolong ^[6]

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1. Univ. Estadual Paulista, Sao Paulo (Brazil)
2. Univ. Cruzeiro do Sul, Sao Paulo (Brazil)
3. Argonne National Lab. (ANL), Argonne, IL (United States)
4. Forschungszentrum Julich and JARA, Julich (Germany)
5. Univ. Autonoma de Barcelona, Bellaterra (Barcelona) (Spain)
6. Univ. of Science and Technology of China, Anhui (People's Republic of China)

Here, 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^±) 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. The two lightest (1/2,1/2^–) doublets fit a different picture: accurate estimates of their masses are obtained by retaining only pseudovector diquarks; in their rest frames, the amplitudes describing their dressed-quark cores contain roughly equal fractions of even- and odd-parity diquarks; and the associated wave functions are predominantly P-wave in nature, but possess measurable S-wave components. Moreover, the first excited state in each negative-parity channel has little of the appearance of a radial excitation. In quantum field theory, all differences between positive- and negative-parity channels must owe to chiral symmetry breaking, which is overwhelmingly dynamical in the light-quark sector. Consequently, experiments that can validate the contrasts drawn herein between the structure of the four lightest (1/2,1/2^±) doublets will prove valuable in testing links between emergent mass generation and observable phenomena and, plausibly, thereby revealing dynamical features of confinement.

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP); USDOE
• Grant/Contract Number: AC02-06CH11357
• OSTI ID: 1480433
• Alternate ID(s): OSTI ID: 1421305
• Journal Information: Physical Review D, Vol. 97, Issue 3; ISSN 2470-0010
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English