The Spin of the Proton

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.

Invited lecture presented at Erice: International School of Nuclear Physics, Course 29, Quarks in Hadrons and Nuclei (September 16-24, 2007)

References in corpus (15)

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• The Deuteron Spin-dependent Structure Function g1d and its First Moment
• Inclusive cross section and double helicity asymmetry for π^0 production in p+p collisions at sqrt(s)=200 GeV: Implications for the polarized gluon distribution in the proton
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• The pion mass dependence of the nucleon form-factors of the energy momentum tensor in the chiral quark-soliton model
• Pion mass dependence of the nucleon mass in the chiral quark soliton model
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• Extraction Of Delta g/g From Hermes Data On Inclusive Charged Hadrons
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Cited by in corpus (18)

• Spin Structure of the Nucleon - Status and Recent Results
• Survey of nucleon electromagnetic form factors
• Beyond the rainbow: effects from pion back-coupling
• The quark-gluon vertex in Landau gauge bound-state studies
• Unquenched quark model for baryons: magnetic moments, spins and orbital angular momenta
• The nucleon's octet axial-charge g_A^8 with chiral corrections
• Strange magnetic form factor of the proton at $Q^2=0.23$ GeV${}^2$
• The Role of Nucleon Strangeness in Supernova Explosions
• Strange magnetic form factor of nucleon in heavy baryon chiral effective approach at next to leading order
• Current quark mass dependence of nucleon magnetic moments and radii
• Low $Q^2$ proton structure function, using gluon and pseudoscalar meson clouds in the constituent quark framework
• Pure sea-quark contributions to the magnetic form factors of $\Sigma$ baryons
• Spin structure of the nucleon: QCD evolution, lattice results and models
• Gluon polarization in the proton
• Relativistic structure of one-meson and one-gluon exchange forces and the lower excitation spectrum of the Nucleon and the Delta
• Spectrum of the excited $N^{\ast }$ and ${\Delta }^{\ast }$ baryons in a relativistic chiral quark model
• Convergence of the self-energy in a relativistic chiral quark model: excited Nucleon and $\Delta$ sector
• Gluonic Colour Singlets in QCD