Why the proton spin is not due to quarks
Recent EMC data on the spin-dependent proton structure function suggest that very little of the proton spin is due to the helicity of the quarks inside it. We argue that, at leading order in the 1/N/sub c/ expansion, none of the proton spin would be carried by quarks in the chiral limit where m/sub q/ = 0. This model-independent result is based on a physical picture of the nucleon as a soliton solution of the effective chiral Lagrangian of large-N/sub c/ QCD. The Skyrme model is then used to estimate quark contribution to the proton spin when chiral symmetry and flavor SU(3) are broken: this contribution turns out to be small, as suggested by the EMC. Next, we discuss the other possible contributions to the proton helicity in the infinite-momentum frame---polarized gluons (..delta..G), and orbital angular momentum (L/sub z/). We argue on general grounds and by explicit example the ..delta..G = 0 and that if the parameters of the chiral Lagrangian are adjusted so that gluons carry /approximately/50% of the proton momentum, most of the orbital angular momentum L/sub z/ is carried by quarks. We mention several experiments to test the EMC results and their interpretation. 43 refs., 3 figs.
- Research Organization:
- Stanford Linear Accelerator Center, Menlo Park, CA (USA)
- DOE Contract Number:
- AC03-76SF00515
- OSTI ID:
- 7182039
- Report Number(s):
- SLAC-PUB-4672; CONF-8806203-2; CONF-8805142-26; ON: DE88015921
- Resource Relation:
- Conference: Symposium on future polarization at Fermilab, Batavia, IL, USA, 13 Jun 1988; Other Information: Portions of this document are illegible in microfiche products
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
PROTONS
QUARK MODEL
GLUONS
LAGRANGIAN FUNCTION
MOMENT OF INERTIA
PARTON MODEL
SPIN ORIENTATION
BARYONS
COMPOSITE MODELS
ELEMENTARY PARTICLES
FERMIONS
FUNCTIONS
HADRONS
MATHEMATICAL MODELS
NUCLEONS
ORIENTATION
PARTICLE MODELS
POSTULATED PARTICLES
645204* - High Energy Physics- Particle Interactions & Properties-Theoretical- Strong Interactions & Properties