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               form Factors Based on a Covariant Quark Model

Ramalho, G.

doi:10.1007/s00601-018-1412-9

Cited by 16 publications

(33 citation statements)

References 95 publications

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“…In our estimates we use the covariant spectator quark model. The covariant spectator quark model has been applied to the studies of the electromagnetic structure of several baryons, including nucleon, octet baryons, and decuplet baryons (including Ω − ) in the spacelike region [34,35,[38][39][40][41][42][43][44][45][46][47][48].…”

Section: Theoretical Modelmentioning

confidence: 99%

Hyperon electromagnetic timelike elastic form factors at large q2

2020

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We present estimates of the hyperon elastic form factors for the baryon octet and the Ω − baryon for large four-momentum transfer squared, q 2 , in the timelike region (q 2 > 0). Experimentally, those form factors can be extracted from the e + e − → BB and pp → BB processes, where B stands for a general baryon. Our results are based on calculations for the elastic electromagnetic form factors in the spacelike region (Q 2 = −q 2 > 0) within a covariant quark model. To connect the results in the spacelike to those in the timelike region, we use asymptotic relations between the two regions which are constraints derived from analyticity and unitarity. We calculate the effective form factors |G(q 2 )|, and compare them with the integrated cross section data σBorn(q 2 ) from BaBar, BES III and CLEO. The available data are at the moment restricted to Λ, Σ 0 , Σ − , Ξ − , Ξ 0 , Ω − as well as to e + e − → ΛΣ 0 and e + e − → Σ 0Λ reactions. Our results provide useful reference for future experiments and seem to indicate that the present data are still in the non-perturbative QCD region, while the onset for the asymptotic constraints from analyticity and unitarity happens much before the region of the pQCD falloff of the form factors.

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Section: Theoretical Modelmentioning

confidence: 99%

Hyperon electromagnetic timelike elastic form factors at large q2

2020

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“…of Eq. (20) includes all the spin structures which contribute both to transitions without parity change (I and iσ 2 ) and with a change in parity (σ 1 and σ 3 ). The integration of the effective current (20) in a product with the spherical functions in the r.h.s.…”

Section: A Spin-orbital Part Of the Matrix Elementmentioning

confidence: 99%

“…(20) includes all the spin structures which contribute both to transitions without parity change (I and iσ 2 ) and with a change in parity (σ 1 and σ 3 ). The integration of the effective current (20) in a product with the spherical functions in the r.h.s. of Eq, (18) and the convolution with "spin-orbital" Clebsch-Gordon coefficients over indices µ ′ l , µ ′ s leads to two different types of transition matrix elements:…”

Section: A Spin-orbital Part Of the Matrix Elementmentioning

confidence: 99%

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Transition form factors and helicity amplitudes for electroexcitation of negative and positive parity nucleon resonances in a light-front quark model

et al. 2019

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A workable basis of quark configurations s 3 , s 2 p and sp 2 at light front has been constructed to describe the high-Q 2 behavior of transition form factors and helicity amplitudes in the electroproduction of the lightest nucleon resonances, N 1/2 − (1535) and N 1/2 + (1440). High-quality data of the CLAS Collaboration are described in the framework of a model which takes into account mixing of the quark configurations and the hadron-molecular states. The model allows for a rough estimate of the quark core weight in the wave function of the resonance in a comparison with high momentum transfer data on resonance electroproduction. I. INTRODUCTIONNew data on the electroproduction of low-lying nucleon resonances (J P = 1 2 ± , 3 2 ± , 5 2 ± ) at large momentum transfer provide important complementary information on the inner structure of hadron resonances [1]- [13]. These data provide evidence in support of the dominance of quark degrees of freedom in the process of electroproduction and allow to evaluate the weight of the quark component in the resonance wave function. The resonance spectrum is remarkably consistent with the quark-model predictions [14], but the traditional quark model refers only to the rest frame, whereas processes at large momentum transfer require a description of baryons in the moving frame. There are many theoretical approaches to the problem which start from the first principles [15]-[35], e.g., light-front QCD [15], lattice QCD [16], quark models [17]-[20], light-cone sum rules [21], approaches based on solution of Dyson-Schwinger and Bethe-Salpeter equations [22, 23], approaches based on chiral dynamics [24], AdS/QCD [26]-[35].The LF wave functions have the advantage that they undergo interaction-independent transformations under the action of "front boosts". In the front form of dynamics [36] the generators of front boosts are kinematical and the front boosts itself are elements of a kinematical subgroup of the Poincaré group. The price to pay is that the space rotations are not kinematical transformations. The light front t−z = 0 is not invariant under space rotations except for rotations about the z axis. Thus the generators of rotations should depend on the interaction given at the light front. By contrast, in the instant form of dynamics the "instant" (t = 0), or canonical, boosts depend on the interaction and do not generate a kinematical subgroup. Then the rotation group (together with the spatial translation group) can be considered as a kinematical subgroup of the Poincaré group.In spite of difficulties associated with the rotational symmetry, the LF approach to the description of the transition form factors implies the construction of a good basis of quark configurations possessing definite values of the orbital (L) and total (J = L + S) angular momenta and satisfying the Pauli exclusion principle. The challenge has been to modify the standard shell-model (normally harmonic oscillator) basis to describe the LF three-quark configurations with simple properties about the relativi...

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“…In the covariant spectator quark model the structure of the baryon wave functions is based on an SU (3) symmetry, which is broken by the quark masses, namely, by the heavier strange quark mass. In the relativistic impulse approximation we can separate the degrees of freedom of the interaction-acting quark from the spectator quark-pair (diquark) and integrate into the internal degrees of freedom of the quark-pair to obtain an effective radial wave function [26][27][28][29][30][31]. Then, the SU (3) symmetry breaking in the model is included at the level of the octet baryon radial wave functions approximated by an S-wave state of the quark-diquark system [13,23].…”

Section: A Valence Quark Contributionmentioning

confidence: 99%

Octet baryon electromagnetic form factor double ratios (GE/GM)/(GE
Ramalho
¹
,
Melo
²
,
Tsushima
³

2019
Phys. Rev. D
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The ratios of the baryon electric (GE) to magnetic (GM ) form factors, GE/GM , can provide us with important information on the structure of baryons in vacuum as demonstrated in recent studies for the proton and neutron systems. It has been argued that the corresponding in-medium ratios, G * E /G * M , can also provide useful information on the electromagnetic structure of baryons in a nuclear medium. Although the ratios may not be measured directly in experiments except for the proton at present, the double ratios (G * E /G * M )/(GE/GM ) can be directly related to the polarization-transfer measurements of bound baryons. In the present work we estimate, for the first time, the double ratios (G * E /G * M )/(GE/GM ) for all the members of octet baryons in symmetric nuclear matter in the range Q 2 = 0-3 GeV 2 , where Q 2 = −q 2 with q being the four-momentum transfer.

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$$N^*$$ N ∗ form Factors Based on a Covariant Quark Model

Cited by 16 publications

References 95 publications

Hyperon electromagnetic timelike elastic form factors at large q2

Hyperon electromagnetic timelike elastic form factors at large q2

Transition form factors and helicity amplitudes for electroexcitation of negative and positive parity nucleon resonances in a light-front quark model

Octet baryon electromagnetic form factor double ratios (GE/GM)/(GE
Ramalho
¹
,
Melo
²
,
Tsushima
³

2019
Phys. Rev. D
Self Cite
12
0
10
0
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$$N^*$$ N ∗ form Factors Based on a Covariant Quark Model

Cited by 16 publications

References 95 publications

Hyperon electromagnetic timelike elastic form factors at large q2

Hyperon electromagnetic timelike elastic form factors at large q2

Transition form factors and helicity amplitudes for electroexcitation of negative and positive parity nucleon resonances in a light-front quark model

Octet baryon electromagnetic form factor double ratios (GE*/GM*)/(GERamalho1, Melo2, Tsushima3 2019Phys. Rev. DSelf Cite120100View full textAdd to dashboardCite

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Octet baryon electromagnetic form factor double ratios (GE/GM)/(GE
Ramalho
¹
,
Melo
²
,
Tsushima
³

2019
Phys. Rev. D
Self Cite
12
0
10
0
View full text Add to dashboard Cite