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 mq = 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 that ..delta..G = 0 and that if the parameters of the chiral Lagrangian are adjusted so that gluons carry /similar to/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.
- Research Organization:
- Stanford Linear Accelerator Center, Stanford University, Stanford, California 94309
- OSTI ID:
- 6188464
- Report Number(s):
- CONF-8805142-; TRN: 89-009087
- Journal Information:
- AIP Conf. Proc.; (United States), Vol. 176:1; Conference: 3. international conference on the intersections between particle and nuclear physics, Rockport, ME, USA, 14 May 1988
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
PROTONS
SPIN
EMC EFFECT
HELICITY
LAGRANGIAN FIELD THEORY
QUANTUM CHROMODYNAMICS
QUARKS
SKYRME POTENTIAL
STRUCTURE FUNCTIONS
SU-3 GROUPS
ANGULAR MOMENTUM
BARYONS
ELEMENTARY PARTICLES
FERMIONS
FIELD THEORIES
FUNCTIONS
HADRONS
LIE GROUPS
NUCLEON-NUCLEON POTENTIAL
NUCLEONS
PARTICLE PROPERTIES
POSTULATED PARTICLES
POTENTIALS
QUANTUM FIELD THEORY
SU GROUPS
SYMMETRY GROUPS
645300* - High Energy Physics- Particle Invariance Principles & Symmetries
645204 - High Energy Physics- Particle Interactions & Properties-Theoretical- Strong Interactions & Properties