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Chiral symmetry and the spin of the proton

1988; Elsevier BV; Volume: 206; Issue: 2 Linguagem: Inglês

10.1016/0370-2693(88)91511-0

1873-2445

Stanley J. Brodsky, John Ellis, Marek Karliner,

High-Energy Particle Collisions Research

Recent EMC data on the spin-dependent proton structure function suggest that very little of the proton spin is due to the helicity of its constituent quarks. We argue that, at leading order in the 1Nc expansion, none of the proton spin would be carried by quarks in the chiral limit where mq=0. This result is derived in the Skyrme model, which is also used to estimate quark contribution to the proton spin when chiral symmetry and SU(3) are broken: this contribution turns out to be small. Therefore, even in the real world most of the proton spin is due to gluons and/or orbital angular momentum, as suggested by the EMC. We mention other experiments to test this suggestion.