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

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.

arXiv comment17 pages, 4 figures, to appear in Nature Review

References in corpus (82)

• Gauge-Invariant Decomposition of Nucleon Spin and Its Spin-Off
• Instantons in QCD
• Deeply Virtual Compton Scattering
• Factorization for hard exclusive electroproduction of mesons in QCD
• Off-Forward Parton Distributions
• Light-Front Holographic QCD and Emerging Confinement
• The Spin Structure of the Nucleon
• Extraction of Spin-Dependent Parton Densities and Their Uncertainties
• The angular momentum controversy: What's it all about and does it matter?
• A first unbiased global determination of polarized PDFs and their uncertainties
• Physics Opportunities with the 12 GeV Upgrade at Jefferson Lab
• Quark Imaging in the Proton Via Quantum Phase-Space Distributions
• Evidence for polarization of gluons in the proton
• Quark helicity distributions in the nucleon for up, down, and strange quarks from semi--inclusive deep--inelastic scattering
• Large-Momentum Effective Theory
• Quark Wigner Distributions and Orbital Angular Momentum
• First simultaneous extraction of spin-dependent parton distributions and fragmentation functions from a global QCD analysis
• Moments of Nucleon Generalized Parton Distributions in Lattice QCD
• Spin and orbital angular momentum in gauge theories: Nucleon spin structure and multipole radiation revisited
• Reply to the Comment on "Spin and orbital angular momentum in gauge theories: Nucleon spin structure and multipole radiation revisited" [PRL 100:232002 (2008)]
• Spin and orbital angular momentum in gauge theories (II): QCD and nucleon spin structure
• Generalized Parton Distributions from Lattice QCD
• The Spin Structure of the Proton
• Notes on the orbital angular momentum of quarks in the nucleon
• The Spin Structure of the Nucleon
• The quark orbital angular momentum from Wigner distributions and light-cone wave functions
• Deeply Virtual Compton Scattering off the neutron
• Transverse Deformation of Parton Distributions and Transversity Decomposition of Angular Momentum
• Complete flavor decomposition of the spin and momentum fraction of the proton using lattice QCD simulations at physical pion mass
• The nucleon spin and momentum decomposition using lattice QCD simulations
• Proton Spin Structure from Measurable Parton Distributions
• FLAVOR-SINGLET g_A FROM LATTICE QCD
• The Spin Structure of the Nucleon in the Asymptotic Limit
• Nucleon form factors and moments of generalized parton distributions using $N_f=2+1+1$ twisted mass fermions
• Precision Measurement of the Longitudinal Double-spin Asymmetry for Inclusive Jet Production in Polarized Proton Collisions at $\sqrt{s}=200$ GeV
• Quark spins and Anomalous Ward Identity
• Quark and Gluon Orbital Angular Momentum and Spin in Hard Processes
• Gluon orbital angular momentum at small-$x$
• NLO Corrections to Deeply-Virtual Compton Scattering
• A critique of the angular momentum sum rules and a new angular momentum sum rule
• Lattice Calculation of Hadronic Light-by-Light Contribution to the Muon Anomalous Magnetic Moment
• The RHIC SPIN Program: Achievements and Future Opportunities
• On Orbital Angular Momentum in Deep Inelastic Scattering
• Measurement of Azimuthal Asymmetries With Respect To Both Beam Charge and Transverse Target Polarization in Exclusive Electroproduction of Real Photons
• Small-$x$ asymptotics of the quark helicity distribution
• Flavour Separation of Helicity Distributions from Deep Inelastic Muon-Deuteron Scattering
• A Lattice Study of Quark and Glue Momenta and Angular Momenta in the Nucleon
• Glue spin and helicity in proton from lattice QCD
• Parton Orbital Angular Momentum and Final State Interactions
• Quark Orbital Angular Momentum from Lattice QCD
• Gluon polarization in the nucleon demystified
• Moments of nucleon generalized parton distributions from lattice QCD
• Physics of Gluon Helicity Contribution to Proton Spin
• Lorentz Symmetry and the Internal Structure of the Nucleon
• Quark Orbital-Angular-Momentum Distribution in the Nucleon
• Longitudinal double-spin asymmetry for inclusive jet and dijet production in $pp$ collisions at $\sqrt{s}=510$ GeV
• Hunting the Gluon Orbital Angular Momentum at the Electron-Ion Collider
• Proton Spin Structure at Small-$x$
• Evolution Equations for Higher Moments of Angular Momentum Distributions
• Gluon Helicity Delta G from a Universality Class of Operators on a Lattice
• Transverse Polarization of the Nucleon in Parton Picture
• Transverse Extension of Partons in the Proton probed by Deeply Virtual Compton Scattering
• Justifying the Naive Partonic Sum Rule for Proton Spin
• The role of the chiral anomaly in polarized deeply inelastic scattering I: Finding the triangle graph inside the box diagram in Bjorken and Regge asymptotics
• Quark orbital dynamics in the proton from Lattice QCD -- from Ji to Jaffe-Manohar orbital angular momentum
• Fundamental Properties of the Proton in Light-Front Zero Modes
• Measurement of the longitudinal spin asymmetries for weak boson production in proton-proton collisions at $\sqrt{s}$ = 510 GeV
• Implications of Color Gauge Symmetry For Nucleon Spin Structure
• Proper identification of the gluon spin
• A Lattice Study of the Magnetic Moment and the Spin Structure of the Nucleon
• Strange and Charm Quark Spins from Anomalous Ward Identity
• Gluon Spin, Canonical Momentum, and Gauge Symmetry
• More on the relation between the two physically inequivalent decompositions of the nucleon spin and momentum
• New relation between transverse angular momentum and generalized parton distributions
• From Ji to Jaffe-Manohar orbital angular momentum in Lattice QCD using a direct derivative method
• Orbital Angular Momentum and Generalized Transverse Momentum Distribution
• The Spin Budget of the Proton at NNLO and Beyond
• Does the Gluon Spin Contribute in A Gauge Invariant Way to Nucleon Spin?
• Transverse spin sum rule of the proton
• QCD evolution of the orbital angular momentum of quarks and gluons: Genuine twist-three part
• Moments of generalized parton distributions and quark angular momentum of the nucleon
• Quark Contributions to Nucleon Momentum and Spin from Domain Wall fermion calculations

Cited by in corpus (6)

• Large-Momentum Effective Theory
• The proton charge radius
• Gluon distributions and their applications to Ioffe-time distributions
• Novel twist-three transverse-spin sum rule for the proton and related generalized parton distributions
• Transverse spin sum rule of the proton
• Neutron Spin Structure from e-3He Scattering with Double Spectator Tagging at the Electron-Ion Collider