Gluon polarization in the proton

Bass, Steven D.; Casey, A.; Thomas, A. W.

doi:10.1103/physrevc.83.038202

Cited by 8 publications

(3 citation statements)

References 37 publications

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“…asy. [464] ∆G 0.4 c-quark axial-charge constraint [465] ∆g/g = −0.13 (21) at • Landau pole, Landau singularity or Landau ghost: the point where a perturbative coupling diverges. At first order (1-loop) in pQCD, this occurs at the scale parameter Λ s .…”

Section: Compass Open Charmmentioning

confidence: 99%

The spin structure of the nucleon

2019

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We review the present understanding of the spin structure of protons and neutrons, the fundamental building blocks of nuclei collectively known as nucleons. The field of nucleon spin provides a critical window for testing Quantum Chromodynamics (QCD), the gauge theory of the strong interactions, since it involves fundamental aspects of hadron structure which can be probed in detail in experiments, particularly deep inelastic lepton scattering on polarized targets.QCD was initially probed in high energy deep inelastic lepton scattering with unpolarized beams and targets. With time, interest shifted from testing perturbative QCD to illuminating the nucleon structure itself. In fact, the spin degrees of freedom of hadrons provide an essential and detailed verification of both perturbative and nonperturbative QCD dynamics.Nucleon spin was initially thought of coming mostly from the spin of its quark constituents, based on intuition from the parton model. However, the first experiments showed that this expectation was incorrect. It is now clear that nucleon physics is much more complex, involving quark orbital angular momenta as well as gluonic and sea quark contributions. Thus, the nucleon spin structure remains a most active aspect of QCD research, involving important advances such as the developments of generalized parton distributions (GPD) and transverse momentum distributions (TMD).Elastic and inelastic lepton-proton scattering, as well as photoabsorption experiments provide various ways to investigate non-perturbative QCD. Fundamental sum rules -such as the Bjorken sum rule for polarized photoabsorption on polarized nucleons -are also in the non-perturbative domain. This realization triggered a vigorous program to link the low energy effective hadronic description of the strong interactions to fundamental quarks and gluon degrees of freedom of QCD. This has also led to advances in lattice gauge theory simulations of QCD and to the development of holographic QCD ideas based on the AdS/CFT or gauge/gravity correspondence, a novel approach providing a well-founded semiclassical approximation to QCD. Any QCD-based model of the nucleon's spin and dynamics must also successfully account for the observed spectroscopy of hadrons. Analytic calculations of the hadron spectrum, a long sought goal of QCD research, has now being realized using light-front holography and superconformal quantum mechanics, a formalism consistent with the results from nucleon spin studies.We begin this review with a phenomenological description of nucleon structure in general and of its spin structure in particular, aimed to engage non-specialist readers. Next, we discuss the nucleon spin structure at high energy, including topics such as 2

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Section: Compass Open Charmmentioning

confidence: 99%

The spin structure of the nucleon

2019

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“…Gluon polarization has been investigated in bag and light-cone models and in studies of heavy-quark axialcharges. The nucleon's charm-quark axial-charge was interpreted to give an estimate of gluon polarization |∆g(m 2 c )| < ∼ 0.3 with α s (m 2 c ) = 0.4 (Bass et al, 2011).…”

Section: Theoretical Understandingmentioning

confidence: 99%

The Spin Structure of the Nucleon

Aidala,

Bass,

Hasch

et al. 2012

Preprint

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“…When comparing our result with Thomas's prediction, we are required to carry out scheme transformation. The gluon polarization in the nucleon has been revealed to be small [36][37][38], which indicates the scheme transformation is unnecessary in this special situation. [Also see Eq.…”

Section: Quark Spin and Orbital Angular Momentum Contributionsmentioning

confidence: 99%

Scale dependencies of proton spin constituents with a nonperturbativeαs

Jia

Huang

2012

Phys. Rev. D

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By introducing the contribution from dynamically generated gluon mass, we present a brand new parametrized form of QCD beta function to get an inferred limited running behavior of QCD coupling constant s . This parametrized form is regarded as an essential factor to determine the scale dependencies of the proton spin constituents at the very low scale. In order to compare with experimental results directly, we work within the gauge-invariant framework to decompose the proton spin. Utilizing the updated nextto-next-leading-order evolution equations for angular momentum observables within a modified minimal subtraction scheme, we indicate that gluon contribution to proton spin cannot be ignored. Specifically, by assuming asymptotic limits of the total quark/gluon angular momentum valid, respectively, the scale dependencies of quark angular momentum J q and gluon angular momentum J g down to Q 2 $ 1 GeV 2 are presented, which are comparable with the preliminary analysis of deeply virtual Compton scattering experiments by HERMES and JLab. After solving scale dependencies of quark spin ÁAE q , orbital angular momenta of quarks L q are given by subtraction, presenting a holistic picture of proton spin partition within up and down quarks at a low scale.

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Gluon polarization in the proton

Abstract: We combine heavy-quark renormalization group arguments with our understanding of the nucleon's wavefunction to deduce a bound on the gluon polarization Delta g in the proton. The bound is consistent with the values extracted from spin experiments at COMPASS and RHIC.Comment: 4 page

Cited by 8 publications

References 37 publications

The spin structure of the nucleon

The spin structure of the nucleon

The Spin Structure of the Nucleon

Scale dependencies of proton spin constituents with a nonperturbativeαs

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