Old and new physics in nucleon spin structure

Abstract

EMC implies quarks carry very little of the proton spin. (G{sub A}/G{sub V}){sub n{yields}p} implies that valence quarks carry 70% of the spin, but disagrees with SU(6). (G{sub A}/G{sub V}){sub {Sigma}{minus}{yields}n} agrees strinkingly with SU(6). All semileptonic decay data can be fit by SU(3), but no model fits the data by breaking SU(6) without also breaking SU(3). Considerable data on hadron masses and magnetic moments are fit by a simple constituent quark model with only constituent quarks. A toy model for the proton with valence quarks and sea fits nearly everything.