Octet Spin Fractions and the Proton Spin Problem

Shanahan, Phiala E.; Thomas, A. W.; Tsushima, K.; Young, R.; Myhrer, F.

doi:10.1103/physrevlett.110.202001

Cited by 19 publications

(25 citation statements)

References 58 publications

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“…However, the experimental value is ∆Σ ≃ 0.33 [8,9], which raised the well known proton spin crises [8][9][10][11]. The above values of ∆Σ q correspond to F = 2 3 and D = 1 [12,13,50,57,123].…”

Section: Su (3) Baryon-meson Modelmentioning

confidence: 92%

“…The method is based on the similarity between the contribution of the meson cloud for the nucleon in our model and CBM [11].…”

Section: B Meson Cloud Dressing Of Octet Baryonsmentioning

confidence: 99%

“…The form factors associated with the weak interaction axial current for the transitions B ′ → B ℓν ℓ , with B, B ′ being spin 1/2 baryons, ℓ = e, µ, τ andν ℓ is a antineutrino, can be decomposed into the axial-vector G A and induced pseudoscalar G P form factors [6,7]. In the limit Q 2 = 0 the octet baryon form factors G A can be related with the polarized deep inelastic scattering data, and used to estimate the spin fraction of the baryon carried by the quarks (valence and sea) [3,[8][9][10][11][12][13].…”

Section: Introductionmentioning

confidence: 99%

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Axial form factors of the octet baryons in a covariant quark model

Ramalho

Tsushima

2016

Phys. Rev. D

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We study the weak interaction axial form factors of the octet baryons, within the covariant spectator quark model, focusing on the dependence of four-momentum transfer squared, Q 2 . In our model the axial form factors GA(Q 2 ) (axial-vector form factor) and GP (Q 2 ) (induced pseudoscalar form factor), are calculated based on the constituent quark axial form factors and the octet baryon wave functions. The quark axial current is parametrized by the two constituent quark form factors, the axial-vector form factor g q A (Q 2 ), and the induced pseudoscalar form factor g q P (Q 2 ). The baryon wave functions are composed of a dominant S-state and a P -state mixture for the relative angular momentum of the quarks. First, we study in detail the nucleon case. We assume that the quark axial-vector form factor g q A (Q 2 ) has the same function form as that of the quark electromagnetic isovector form factor. The remaining parameters of the model, the P -state mixture and the Q 2 -dependence of g q P (Q 2 ), are determined by a fit to the nucleon axial form factor data obtained by lattice QCD simulations with large pion masses. In this lattice QCD regime the meson cloud effects are small, and the physics associated with the valence quarks can be better calibrated. Once the valence quark model is calibrated, we extend the model to the physical regime, and use the low Q 2 experimental data to estimate the meson cloud contributions for GA(Q 2 ) and GP (Q 2 ). Using the calibrated quark axial form factors, and the generalization of the nucleon wave function for the other octet baryon members, we make predictions for all the possible weak interaction axial form factors GA(Q 2 ) and GP (Q 2 ) of the octet baryons. The results are compared with the corresponding experimental data for GA(0), and with the estimates of baryon-meson models based on SU (6) symmetry.

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Section: Su (3) Baryon-meson Modelmentioning

confidence: 92%

“…The method is based on the similarity between the contribution of the meson cloud for the nucleon in our model and CBM [11].…”

Section: B Meson Cloud Dressing Of Octet Baryonsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Axial form factors of the octet baryons in a covariant quark model

Ramalho

Tsushima

2016

Phys. Rev. D

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“…Thus, we now have quite accurate determinations of the hyperon electric [22] and magnetic [23] form factors up to 1.4 GeV 2 , as well as low moments of their parton distribution functions [24]. It has even been possible recently to shed some light on the proton spin puzzle [25,26] by calculating the spin fractions carried by quarks across the octet [27].…”

Section: Introductionmentioning

confidence: 97%

SU(3)-flavor breaking in octet baryon masses and axial couplings

2014

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The lightest baryon octet is studied within a covariant and confining Nambu-Jona-Lasinio model. By solving the Poincaré covariant Faddeev equations -including scalar and axialvector diquarkswe determine the baryon octet masses and axial charges for strangeness conserving transitions. For the axial charges the degree of violation of SU (3) flavour symmetry, arising because of the strange spectator quark(s), is found to be no more than 10%.

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“…18 Figure 4, taken from Ref., 18 illustrates that the quark spin fraction is environment dependent. The figure clearly highlights that this result is evident in the bare lattice results, with considerable enhancement seen in the extrapolation to the physical point.…”

Section: Octet Baryon Spin Fractionsmentioning

confidence: 99%

Progress in resolving charge symmetry violation in nucleon structure

Young

Shanahan

Thomas

2014

Int. J. Mod. Phys. E

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Recent work unambiguously resolves the level of charge symmetry violation in moments of parton distributions using 2 + 1−flavor lattice QCD. We introduce the methods used for that analysis by applying them to determine the strong contribution to the proton-neutron mass difference. We also summarize related work which reveals that the fraction of baryon spin which is carried by the quarks is in fact structure-dependent rather than universal across the baryon octet.

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Octet Spin Fractions and the Proton Spin Problem

Cited by 19 publications

References 58 publications

Axial form factors of the octet baryons in a covariant quark model

Axial form factors of the octet baryons in a covariant quark model

SU(3)-flavor breaking in octet baryon masses and axial couplings

Progress in resolving charge symmetry violation in nucleon structure

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