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Title: Electroexcitation of nucleon resonances

Abstract

We review recent progress in the investigation of the electroexcitation of nucleon resonances, both in experiment and in theory. The most accurate results have been obtained for the electroexcitation amplitudes of the four lowest excited states, which have been measured in a range of Q2 up to 8 and 4.5 GeV2 for the Delta(1232)P33, N(1535)S11 and N(1440)P11, N(1520)D13, respectively. These results have been confronted with calculations based on lattice QCD, large-Nc relations, perturbative QCD (pQCD), and QCD-inspired models. The amplitudes for the Delta(1232) indicate large pion-cloud contributions at low Q2 and don't show any sign of approaching the pQCD regime for Q2<7 GeV2. Measured for the first time, the electroexcitation amplitudes of the Roper resonance, N(1440)P11, provide strong evidence for this state as a predominantly radial excitation of a three-quark (3q) ground state, with additional non-3-quark contributions needed to describe the low Q2 behavior of the amplitudes. The longitudinal transition amplitude for the N(1535)S11 was determined and has become a challenge for quark models. Explanations may require large meson-cloud contributions or alternative representations of this state. The N(1520)D13 clearly shows the rapid changeover from helicity-3/2 dominance at the real photon point to helicity-1/2 dominance at Q2 > 0.5 GeV2, confirmingmore » a long-standing prediction of the constituent quark model. The interpretation of the moments of resonance transition form factors in terms of transition transverse charge distributions in infinite momentum frame is presented.« less

Authors:
Publication Date:
Research Org.:
Thomas Jefferson National Accelerator Facility, Newport News, VA (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1029532
Report Number(s):
JLAB-PHY-11-1409; DOE/OR/23177-1728; arXiv:1109.1720
Journal ID: ISSN 0146-6410; PPNPDB; TRN: US1200849
DOE Contract Number:  
AC05-06OR23177
Resource Type:
Journal Article
Resource Relation:
Journal Name: Progress in Particle and Nuclear Physics; Journal Volume: 67; Journal Issue: 1
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; AMPLITUDES; CHARGE DISTRIBUTION; EXCITATION; EXCITED STATES; FORECASTING; FORM FACTORS; GROUND STATES; N-1440 BARYONS; NUCLEONS; PHOTONS; QUANTUM CHROMODYNAMICS; QUARK MODEL; RESONANCE; TRANSITION AMPLITUDES

Citation Formats

Inna Aznauryan, Volker D. Burkert. Electroexcitation of nucleon resonances. United States: N. p., 2012. Web. doi:10.1016/j.ppnp.2011.08.001.
Inna Aznauryan, Volker D. Burkert. Electroexcitation of nucleon resonances. United States. doi:10.1016/j.ppnp.2011.08.001.
Inna Aznauryan, Volker D. Burkert. Sun . "Electroexcitation of nucleon resonances". United States. doi:10.1016/j.ppnp.2011.08.001. https://www.osti.gov/servlets/purl/1029532.
@article{osti_1029532,
title = {Electroexcitation of nucleon resonances},
author = {Inna Aznauryan, Volker D. Burkert},
abstractNote = {We review recent progress in the investigation of the electroexcitation of nucleon resonances, both in experiment and in theory. The most accurate results have been obtained for the electroexcitation amplitudes of the four lowest excited states, which have been measured in a range of Q2 up to 8 and 4.5 GeV2 for the Delta(1232)P33, N(1535)S11 and N(1440)P11, N(1520)D13, respectively. These results have been confronted with calculations based on lattice QCD, large-Nc relations, perturbative QCD (pQCD), and QCD-inspired models. The amplitudes for the Delta(1232) indicate large pion-cloud contributions at low Q2 and don't show any sign of approaching the pQCD regime for Q2<7 GeV2. Measured for the first time, the electroexcitation amplitudes of the Roper resonance, N(1440)P11, provide strong evidence for this state as a predominantly radial excitation of a three-quark (3q) ground state, with additional non-3-quark contributions needed to describe the low Q2 behavior of the amplitudes. The longitudinal transition amplitude for the N(1535)S11 was determined and has become a challenge for quark models. Explanations may require large meson-cloud contributions or alternative representations of this state. The N(1520)D13 clearly shows the rapid changeover from helicity-3/2 dominance at the real photon point to helicity-1/2 dominance at Q2 > 0.5 GeV2, confirming a long-standing prediction of the constituent quark model. The interpretation of the moments of resonance transition form factors in terms of transition transverse charge distributions in infinite momentum frame is presented.},
doi = {10.1016/j.ppnp.2011.08.001},
journal = {Progress in Particle and Nuclear Physics},
number = 1,
volume = 67,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2012},
month = {Sun Jan 01 00:00:00 EST 2012}
}