The spin of the proton

2008/01/07 by A. W. Thomas, Jefferson Lab · 1 citation
Physics and Astronomy · #Anomaly (physics) #Gluon #High-Energy Particle Collisions Research #Muon #Nuclear physics #Nucleon #Particle physics #Particle physics theoretical and experimental studies #Physics #Proton #Proton spin crisis #Quantum Chromodynamics and Particle Interactions #Quantum mechanics #Quark #Spin (aerodynamics) #hep-ph

paper · pdf · doi:10.1016/j.ppnp.2007.12.039

published as Prog.Part.Nucl.Phys.61:219-228,2008 · Invited lecture presented at Erice: International School of Nuclear Physics, Course 29, Quarks in Hadrons and Nuclei (September 16-24, 2007)

openalex publication_date 2008/01/07 · arxiv created 2008/05/28 · arxiv updated 2010/11/11 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05

Abstract

The twenty years since the announcement of the proton spin crisis by the European Muon Collaboration has seen tremendous progress in our knowledge of the distribution of spin within the proton. The problem is reviewed, beginning with the original data and the suggestion that polarized gluons may play a crucial role in resolving the problem through the U(1) axial anomaly. The discussion continues to the present day where not only have strong limits have been placed on the amount of polarized glue in the proton but the experimental determination of the spin content has become much more precise. It is now clear that the origin of the discrepancy between experiment and the naive expectation of the fraction of spin carried by the quarks and anti-quarks in the proton lies in the non-perturabtive structure of the proton. We explain how the features expected in a modern, relativistic and chirally symmetric description of nucleon structure naturally explain the current data.

Citations

• Spin asymmetry A1d and the spin-dependent structure function g1d of the deuteron at low values of x and Q2
• Pion mass dependence of the nucleon form factors of the energy-momentum tensor in the chiral quark-soliton model
• Heavy-quark axial charges to nonleading order
• Nucleon magnetic moments beyond the perturbative chiral regime
• Chiral analysis of quenched baryon masses
• Physical Nucleon Properties from Lattice QCD
• Extrapolation of lattice QCD results beyond the power-counting regime
• Chiral extrapolation of hadronic observables
• Testing the Standard Model by Precision Measurement of the Weak Charges of Quarks
• Extracting Nucleon Strange and Anapole Form Factors from World Data
• Chiral Symmetry and the Intrinsic Structure of the Nucleon
• Gluon polarization in the nucleon from quasi-real photoproduction of high-pT hadron pairs
• Strange Electric Form Factor of the Proton
• Axial-Vector Vertex in Spinor Electrodynamics
• How to Renormalize the Schrodinger Equation

Cited by

• A relativistic structure of one-meson and one-gluon exchange forces and a lower excitation spectrum of the nucleon and Δ