Electromagnetic transition form factors of baryons in the space-like momentum region

Sanchis-Alepuz, Hèlios; Alkofer, Reinhard; Fischer, Christian

doi:10.1140/epja/i2018-12465-x

Cited by 26 publications

(25 citation statements)

References 91 publications

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“…1. Our results compare with the outcome of other theoretical predictions coming from constituent-quark models [10,11,12]. For Q 2 0.5 GeV 2 our predictions for G * M agree well with the data, for vanishing Q 2 , however, we underestimate the data by about 15% for model I and about 25% for model II.…”

Section: Resultssupporting

confidence: 87%

Pion-Cloud Contribution to the $$N\rightarrow \varDelta $$ Transition Form Factors

Jung

Schweiger

2020

Recent Progress in Few-Body Physics

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We examine the contribution of the pion cloud to the electromagnetic N → ∆ transition form factors within a relativistic hybrid constituent-quark model. In this model baryons consist not only of the 3q valence component, but contain, in addition, a 3qπ non-valence component. We start with constituent quarks which are subject to a scalar, isoscalar confining force. This leads to an SU (6) spin-flavor symmetric spectrum with degenerate nucleon and Delta masses. Mass splitting is caused by pions which are assumed to couple directly to the quarks. The point-form of relativistic quantum mechanics is employed to achieve a relativistically invariant description of this system. The N → ∆ transition current is then determined from the one-photon exchange contribution to the ∆ electroproduction amplitude. We will give predictions for the ratios REM and RSM of electric to magnetic and Coulomb to magnetic form factors, which are supposed to be most sensitive to pion-cloud effects.

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Section: Resultssupporting

confidence: 87%

Pion-Cloud Contribution to the $$N\rightarrow \varDelta $$ Transition Form Factors

Jung

Schweiger

2020

Recent Progress in Few-Body Physics

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“…Regarding the nucleon mass, it revealed that the quark-diquark picture is accurate at the level of 5%. A variety of applications ensued: nucleon electromagnetic form factors [61]; masses of the ∆-and Ω-baryons [62]; nucleon axial and pseudoscalar form factors [63]; a spectrum of ground-state octet and decuplet baryons [64] and their electromagnetic form factors [65]; masses of low-lying nucleon excited states [66]; and electromagnetic transition form factors between ground-state octet and decuplet baryons [67]. Significant algebraic and computational effort was required to complete these studies; and the results are instructive and promising, indicating that the framework is potentially capable of drawing a traceable connection between QCD and the many baryon observables that are being made accessible by modern facilities.…”

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confidence: 99%

Spectrum of Light- and Heavy-Baryons

2019

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A symmetry-preserving truncation of the strong-interaction bound-state equations is used to calculate the spectrum of ground-state J = 1/2 + , 3/2 + (qq q )-baryons, where q, q , q ∈ {u, d, s, c, b}, their first positive-parity excitations and parity partners. Using two parameters, a description of the known spectrum of 39 such states is obtained, with a mean-absolute-relativedifference between calculation and experiment of 3.6(2.7)%. From this foundation, the framework is subsequently used to predict the masses of 90 states not yet seen empirically.Keywords Poincaré-covariant Faddeev equation · baryon spectrum · light and heavy quarks · Dyson-Schwinger equations · emergence of mass 1 IntroductionThe Faddeev equation was introduced almost sixty years ago [1]. It treats the quantum mechanical problem of three-bodies interacting via pairwise potentials by reducing it to a sum of three terms, each of which describes a solvable scattering problem in distinct two-body subsystems. The Faddeev formulation of that three-body problem has a unique solution.An analogous approach to the three-valence-quark (baryon) bound-state problem in quantum chromodynamics (QCD) was explained in Refs. [2][3][4][5][6]. In this case, owing to dynamical mass generation, expressed most simply in QCD's one-body Schwinger functions in the gauge [7][8][9][10][11][12][13][14][15][16][17][18] and matter sectors [19][20][21][22][23][24], and the importance of symmetries [25][26][27], one requires a Poincaré-covariant quantum field theory generalisation of the Faddeev equation. Like the Bethe-Salpeter equation for mesons, it is natural to consider such a Faddeev equation as one of the tower of QCD's Dyson-Schwinger equations (DSEs) [28], which are being used to develop a systematic, symmetry-preserving, continuum approach to the strong-interaction bound-state problem [29][30][31][32][33][34].The Poincaré-covariant Faddeev equation for baryons is typically treated in a quark-diquark approximation, where the diquark correlations are nonpointlike and dynamical [35]. This amounts to a simplified treatment of the scattering problem in the two-body subchannels (as explained, e.g. in Ref. [36], Sec. II.A.2), which is founded on an observation that the same interaction which describes

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“…Model calculations and large-N c estimates also suggest a small valence-quark contribution to R EM and R SM , indicating that these ratios may be dominated by pion-cloud effects [112][113][114][115][116]. By contrast, in Dyson-Schwinger calculations the valence-quark components are significant due to relativistic effects [28,[117][118][119]. Eq.…”

Section: N(1650)mentioning

confidence: 98%

Nucleon resonances in Compton scattering

Eichmann

Ramalho

2018

Phys. Rev. D

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We calculate the nucleon resonance contributions to nucleon Compton scattering, including all states with J P = 1/2 ± and J P = 3/2 ± where experimental data for their electromagnetic transition form factors exist. To this end, we construct a tensor basis for the Compton scattering amplitude based on electromagnetic gauge invariance, crossing symmetry and analyticity. The corresponding Compton form factors provide a Lorentz-invariant description of the process in general kinematics, which reduces to the static and generalized polarizabilities in the appropriate kinematic limits. We derive the general forms of the offshell nucleon-to-resonance transition vertices that implement electromagnetic and spin-3/2 gauge invariance, which automatically also defines onshell transition form factors that are free of kinematic constraints. We provide simple fits for those form factors, which we use to analyze the resulting Compton form factors and extract their contributions to the nucleon's polarizabilities. Apart from the ∆(1232), the resonance contributions to the scalar and spin polarizabilites are very small, although the N (1520) could play a role for the proton's magnetic polarizability.

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Electromagnetic transition form factors of baryons in the space-like momentum region

Cited by 26 publications

References 91 publications

Pion-Cloud Contribution to the $$N\rightarrow \varDelta $$ Transition Form Factors

Pion-Cloud Contribution to the $$N\rightarrow \varDelta $$ Transition Form Factors

Spectrum of Light- and Heavy-Baryons

Nucleon resonances in Compton scattering

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