<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mo>&lt;</mml:mo><mml:mi>‘</mml:mi><mml:mrow><mml:msup><mml:mrow><mml:mi>γ</mml:mi></mml:mrow><mml:mrow><mml:mi>*</mml:mi></mml:mrow></mml:msup></mml:mrow><mml:mrow><mml:mrow><mml:mover><mml:mrow><mml:mi>N</mml:mi></mml:mrow><mml:mrow><mml:mo>→</mml:mo></mml:mrow></mml:mover></mml:mrow></mml:mrow><mml:mi>Δ</mml:mi></mml:math>transition form factors: A new analysis of data on<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"

Kamalov, S.S.; Yang, Shin Nan; Drechsel, D.; Hanstein, O.; Tiator, L.

doi:10.1103/physrevc.64.032201

Cited by 148 publications

(144 citation statements)

References 30 publications

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“…Very close results are obtained within the dynamical model of Refs. [25,26]. The meson-cloud contribution makes up more than 30% of the total amplitude at the photon point and remains sizable while Q 2 increases.…”

Section: A (1232) P 33 Resonancementioning

confidence: 99%

“…[18]. Within dynamical reaction models [25][26][27][28], the meson-cloud contribution was identified as the source of this discrepancy. The importance of the pion (cloud) contribution for the γ * p → (1232)P 33 transition is confirmed also by the lattice QCD calculations [29].…”

Section: A (1232) P 33 Resonancementioning

confidence: 99%

“…In the case of the N (1440)P 11 and N (1535)S 11 , the mass ordering of these states, the large total width of N (1440)P 11 , and the substantial coupling of N (1535)S 11 to the ηN channel [20] and to strange particles [21,22] are indicative of possible additional qq components in the wave functions of these states [23,24] and/or of alternative descriptions. Within dynamical reaction models [25][26][27][28], the meson-cloud contribution is identified as a source of the long-standing discrepancy between the data and constituent quark model predictions for the γ * N → (1232)P 33 magnetic-dipole amplitude. The importance of pion (cloud) contributions to the transition form factors has also been confirmed by the lattice calculations [29].…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Electroexcitation of nucleon resonances from CLAS data on single pion electroproduction

Aznauryan¹,

Burkert²,

Biselli³

et al. 2009

Phys. Rev. C

250

380

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We present results on the electroexcitation of the low mass resonances (1232)P 33 , N (1440)P 11 , N (1520)D 13 , and N (1535)S 11 in a wide range of Q 2 . The results were obtained in the comprehensive analysis of data from the Continuous Electron Beam Accelerator Facility (CEBAF) large acceptance spectrometer (CLAS) detector at the Thomas Jefferson National Accelerator Facility (JLab) on differential cross sections, longitudinally polarized beam asymmetries, and longitudinal target and beam-target asymmetries for π electroproduction off the proton. The data were analyzed using two conceptually different approaches-fixed-t dispersion relations and a unitary isobar model-allowing us to draw conclusions on the model sensitivity of the obtained electrocoupling amplitudes. The amplitudes for the (1232)P 33 show the importance of a meson-cloud contribution to quantitatively explain the magnetic dipole strength, as well as the electric and scalar quadrupole transitions. They do not show any tendency of approaching the pQCD regime for Q 2 6 GeV 2 . For the Roper resonance, N (1440)P 11 , the data provide strong evidence that this state is a predominantly radial excitation of a three-quark (3q) ground state. Measured in pion electroproduction, the transverse helicity amplitude for the N (1535)S 11 allowed us to obtain the branching ratios of this state to the πN and ηN channels via comparison with the results extracted from η electroproduction. The extensive CLAS data also enabled the extraction of the γ * p → N (1520)D 13 and N (1535)S 11 longitudinal helicity amplitudes with good precision. For the N (1535)S 11 , these results became a challenge for quark models and may be indicative of large meson-cloud contributions or of representations of this state that differ from a 3q excitation. The transverse amplitudes for the N (1520)D 13 clearly show the rapid changeover from helicity-3/2 dominance at the real photon point to helicity-1/2 dominance at Q 2 > 1 GeV 2 , confirming a long-standing prediction of the constituent quark model.

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Section: A (1232) P 33 Resonancementioning

confidence: 99%

Section: A (1232) P 33 Resonancementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Electroexcitation of nucleon resonances from CLAS data on single pion electroproduction

Aznauryan¹,

Burkert²,

Biselli³

et al. 2009

Phys. Rev. C

250

380

View full text Add to dashboard Cite

show abstract

“…Among those are the Sato-Lee model [70], which has been extended by the EBAC [71][72][73] and ANL/Osaka collaborations [74] and extensively applied to analyze pion photo-and electroproduction data. The Dubna-Mainz-Taiwan (DMT) [75,76], Valencia [77], Jülich-Bonn [78,79] and GSI models [80][81][82] have been developed along similar lines. Theoretical constraints like unitarity and analyticity of the S-matrix are manifest in these approaches.…”

Section: Helicity Amplitudes Vs Transition Form Factorsmentioning

confidence: 99%

Baryons as relativistic three-quark bound states

Eichmann

Sanchis-Alepuz

Williams

et al. 2016

Progress in Particle and Nuclear Physics

417

530

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We review the spectrum and electromagnetic properties of baryons described as relativistic three-quark bound states within QCD. The composite nature of baryons results in a rich excitation spectrum, whilst leading to highly non-trivial structural properties explored by the coupling to external (electromagnetic and other) currents. Both present many unsolved problems despite decades of experimental and theoretical research. We discuss the progress in these fields from a theoretical perspective, focusing on nonperturbative QCD as encoded in the functional approach via Dyson-Schwinger and Bethe-Salpeter equations. We give a systematic overview as to how results are obtained in this framework and explain technical connections to lattice QCD. We also discuss the mutual relations to the quark model, which still serves as a reference to distinguish 'expected' from 'unexpected' physics. We confront recent results on the spectrum of non-strange and strange baryons, their form factors and the issues of two-photon processes and Compton scattering determined in the DysonSchwinger framework with those of lattice QCD and the available experimental data. The general aim is to identify the underlying physical mechanisms behind the plethora of observable phenomena in terms of the underlying quark and gluon degrees of freedom.

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“…At the experimentally accessible energies, however, the asymptotic scaling behavior of the FFs seems not to be apparent. For instance, the measurements of the electromagnetic ratio R EM (Q 2 ) of the ∆(1232) resonance [6,7,8,9,10,11,12,13,14] indicate that it remains to be small and negative up to the momentum transfer Q 2 = 7 GeV 2 , which disagrees sharply with the pQCD scaling R EM (Q 2 → +∞) = +1 [16,17]. It is possible that the transition to the scaling may not occur up to extremely large momentum transfers Q 2 ≫ 20 GeV 2 [18,19].…”

Section: Introductionmentioning

confidence: 99%

Low-Q2 scaling behavior of the form-factor ratios for the NΔ(1232)-transition

Vereshkov

Volchanskiy

2010

Physics Letters B

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We address the issue of the scaling behavior of the nucleon electromagnetic form factors (FFs). We propose a consistent Lagrangian of the electromagnetic N∆ (1232)-interaction possessing all the internal symmetries of the spin-3 2 baryon resonance, point and gauge invariance. The point and gauge invariant FFs may exhibit quasi-scaling behavior-while the FFs do not reach asymptotic scaling domain, the ratios thereof do. The hypothesis of the quasi-scaling is in good agreement with the experimental data available at Q 2 0.4 GeV 2 .

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<‘γ*N→Δtransition form factors: A new analysis of data on

Cited by 148 publications

References 30 publications

Electroexcitation of nucleon resonances from CLAS data on single pion electroproduction

Electroexcitation of nucleon resonances from CLAS data on single pion electroproduction

Baryons as relativistic three-quark bound states

Low-Q2 scaling behavior of the form-factor ratios for the NΔ(1232)-transition

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