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Proton spin after 30 years: what we know and what we don't?

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arxiv 2009.01291 v1 pith:BVVAJK5M submitted 2020-09-02 hep-ph hep-exhep-latnucl-exnucl-th

classification hep-phhep-exhep-latnucl-exnucl-th
keywords whatprotonspinexperimentalfirstgluonangularbeen
verification ladder T0 review T1 audit T2 compute T3 formal
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abstract

More than three decades has passed since the European Muon Collaboration published the first surprising result on the spin structure of the proton. Much theoretical and experimental progress has been made in understanding the origins of the proton spin. In this review, we will discuss what we have learned so far, what are still missing, and what we shall expect to learn from the upcoming experiments including JLab 12 GeV and Electron-Ion Collider. In particular, we focus on first principles calculations and experimental measurements of the total gluon helicity $\Delta G$, and quark and gluon orbital angular momenta.

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Cited by 10 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. Analytic Solution for the Helicity Evolution Equations at Small $x$ and Large $N_c\&N_f$

    hep-ph 2025-07 conditional novelty 7.0 of 10

    An exact analytic solution of the revised large-Nc and large-Nf small-x helicity evolution equations in QCD, yielding all-order polarized DGLAP anomalous dimensions and small-x growth intercepts.

  2. Universal features of high-energy scattering of Laguerre-Gaussian states

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    Nonzero impact parameter between two paraxial LG vortex packets produces universal P_perp effects (vortex splitting, high-contrast fringes, momentum imbalance) that make b a useful experimental probe rather than a nuisance.

  3. Spin and momentum fraction carried by partons in the nucleon

    hep-lat 2026-07 conditional novelty 6.0 of 10

    Lattice QCD at physical quark masses, extrapolated to the continuum, yields total proton momentum fraction 0.995(60)(29) and spin 0.507(43)(65), satisfying both sum rules and giving the first complete flavor decomposi...

  4. Relativistic spin hydrodynamics with antisymmetric spin tensors and an extension of the Bargmann-Michel-Telegdi equation

    nucl-th 2025-06 conditional novelty 6.0 of 10

    A new entropy-principle formulation of relativistic spin hydrodynamics yields a modified BMT spin evolution equation and spin-induced transport corrections that map onto inverse and anomalous Hall effects.

  5. Extraction of $\sigma_{TT}$ for Proton, Neutron, Deuteron and $^3$He from Quasi-real Photon Scattering

    hep-ex 2026-07 conditional novelty 5.0 of 10

    Quasi-real electroproduction data extrapolated to Q²=0 give σ_TT for p, n, d and ³He, with larger neutron/deuteron Δ(1232) strength than real-photon data and better isospin consistency.

  6. Toward Precision Helicity PDFs from Global DIS and SIDIS Fits with Projected EIC Measurements

    hep-ph 2026-02 conditional novelty 4.0 of 10

    Projected EIC pion and kaon SIDIS measurements would substantially reduce the uncertainties on the proton's sea-quark and gluon helicity distributions, most strongly at small momentum fractions.

  7. Anomalies, Topology, and Hadron Structure in QCD

    hep-ph 2026-06 conditional novelty 3.0 of 10

    A review unifying the QCD axial and trace anomalies with vacuum topology, arguing that the proton spin puzzle and the U(1)_A problem are both controlled by topological screening encoded in the susceptibility slope χ′(0).

  8. Global analyses of helicity-dependent parton distribution functions

    hep-ph 2026-07 accept novelty 2.0 of 10

    Modern global QCD analyses agree that up-quark helicity is positive and down-quark helicity negative, with positive gluon polarisation at moderate x, while the full gluon spin moment remains limited by the unmeasured ...

  9. Spin Structure of the Nucleon: Overview

    hep-ph 2026-07 unverdicted

    A pedagogical review consolidates the proton spin decomposition into quark/gluon spin and orbital angular momentum, emphasizing gauge-invariant OAM definitions, small-x cancellations, and EIC observables.

  10. The equation of state for neutron stars

    nucl-th 2026-07 unverdicted

    A textbook-style review of the neutron-star equation of state covering the models, experimental and observational constraints, and open questions, with no new result claimed or derived.

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