Electroproduction of pions near the Δ (1236) isobar and the form factor G∗M (q2) of the (γNΔ)-vertex

Bartel, W.; Dudelzak, B.; Krehbiel, H.; McElroy, J.; Meyer‐Berkhout, U.; Schmidt, W.; Walther, Valentin; Weber, G.

doi:10.1016/0370-2693(68)90155-x

Cited by 128 publications

(47 citation statements)

References 17 publications

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“…); CI result [21,22] (dotted, blue); dressed-quark core contribution inferred using SL-model [24] (dot-dashed, green); and data from Refs. [8,[133][134][135][136][137], whose errors are commensurate with the point size. Right panel.…”

Section: Approachmentioning

confidence: 88%

Nucleon and $${\Delta}$$ Δ Elastic and Transition Form Factors

et al. 2014

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We present a unified study of nucleon and ∆ elastic and transition form factors, and compare predictions made using a framework built upon a Faddeev equation kernel and interaction vertices that possess QCD-like momentum dependence with results obtained using a symmetry-preserving treatment of a vector ⊗ vector contact-interaction. The comparison emphasises that experiments are sensitive to the momentum dependence of the running couplings and masses in the strong interaction sector of the Standard Model and highlights that the key to describing hadron properties is a veracious expression of dynamical chiral symmetry breaking in the bound-state problem. Amongst the results we describe, the following are of particular interest:possesses a zero at Q 2 = 9.5 GeV 2 ; any change in the interaction which shifts a zero in the proton ratio to larger Q 2 relocates a zero inthere is likely a value of momentum transfer above which G n E > G p E ; and the presence of strong diquark correlations within the nucleon is sufficient to understand empirical extractions of the flavour-separated form factors. Regarding the ∆(1232)-baryon, we find that, inter alia: the electric monopole form factor exhibits a zero; the electric quadrupole form factor is negative, large in magnitude, and sensitive to the nature and strength of correlations in the ∆(1232) Faddeev amplitude; and the magnetic octupole form factor is negative so long as rest-frame P -and D-wave correlations are included. In connection with the N → ∆ transition, the momentum-dependence of the magnetic transition form factor, G * M , matches that of G n M once the momentum transfer is high enough to pierce the meson-cloud; and the electric quadrupole ratio is a keen measure of diquark and orbital angular momentum correlations, the zero in which is obscured by meson-cloud effects on the domain currently accessible to experiment. Importantly, within each framework, identical propagators and vertices are sufficient to describe all properties discussed herein. Our analysis and predictions should therefore serve as motivation for measurement of elastic and transition form factors involving the nucleon and its resonances at high photon virtualities using modern electron-beam facilities.

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Section: Approachmentioning

confidence: 88%

Nucleon and $${\Delta}$$ Δ Elastic and Transition Form Factors

et al. 2014

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“…Á reaction, including the total, and the contributions from the bare core (valence quark), and the pion cloud, as well as the data for Ã p ! Á þ from DESY [62], SLAC [63], CLAS/Jefferson …”

Section: A Octet To Decuplet Electromagnetic Transition Form Factorsmentioning

confidence: 99%

Octet to decuplet electromagnetic transition in a relativistic quark model

Ramalho

Tsushima

2013

Phys. Rev. D

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We study the octet to decuplet baryon electromagnetic transitions using the covariant spectator quark model and predict the transition magnetic dipole form factors for those involving the strange baryons. Utilizing SU (3) symmetry, the valence quark contributions are supplemented by the pion cloud dressing based on the one estimated in the γ * N → ∆ reaction. Although the valence quark contributions are dominant in general, the pion cloud effects turn out to be very important to describe the experimental data. We also show that other mesons besides the pion in particular the kaon, may be relevant for some reactions such as γ * Σ + → Σ * + , based on our analysis for the radiative decay widths of the strange decuplet baryons.

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“…(6.12), to the G * M experimental data [11,12,53,54] and of the bare component, to the bare "data" for Q 2 < 2 GeV 2 based on the SL extraction [41, 52] discussed above. The parameters for Models I and II are compared to models I(B) and II(B) in Table II given there is for the fit to G * M only.)…”

Section: A Decomposition Into Bare and Pion Cloud Form Factorsmentioning

confidence: 99%

A covariant model for the nucleon and the Δ

2008

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The covariant spectator formalism is used to model the nucleon and the ∆(1232) as a system of three constituent quarks with their own electromagnetic structure. The definition of the "fixed-axis" polarization states for the diquark emitted from the initial state vertex and absorbed into the final state vertex is discussed. The helicity sum over those states is evaluated and seen to be covariant. Using this approach, all four electromagnetic form factors of the nucleon, together with the magnetic form factor, G * M , for the γN → ∆ transition, can be described using manifestly covariant nucleon and ∆ wave functions with zero orbital angular momentum L, but a successful description of G * M near Q 2 = 0 requires the addition of a pion cloud term not included in the class of valence quark models considered here. We also show that the pure S-wave model gives electric, G * E , and coulomb, G * C , transition form factors that are identically zero, showing that these form factors are sensitive to wave function components with L > 0.

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Electroproduction of pions near the Δ (1236) isobar and the form factor G∗M (q2) of the (γNΔ)-vertex

Cited by 128 publications

References 17 publications

Nucleon and $${\Delta}$$ Δ Elastic and Transition Form Factors

Nucleon and $${\Delta}$$ Δ Elastic and Transition Form Factors

Octet to decuplet electromagnetic transition in a relativistic quark model

A covariant model for the nucleon and the Δ

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