Gluons and the spin of the proton
Abstract
The recent observation that constituent quark helicities carry very little of the spin of the proton, in contrast with naive quark model expectations, can be understood by taking into account nonperturbative aspects of QCD, such as chiral symmetry breaking and confinement. We compute the nonstrange quark contribution ∆u+∆d to the proton spin in a chiral fieldtheoretical model of quark and gluon confinement. Our mean field computations include selfconsistently the effects of gluon exchange between constituent quarks. When the parameters of the model, including the effective strong fine structure constant α_{s}, are adjusted to reproduce as far as possible the experimental mean nucleondelta mass and the relative nucleondelta mass splitting, we obtain ∆u+∆d⋍0.26, which is only one third of the α_{s}=0 value. We show that this implies that all the proton spin is in fact orbital angular momentum.
 Publication:

Physics Letters B
 Pub Date:
 March 1989
 DOI:
 10.1016/03702693(89)900440
 Bibcode:
 1989PhLB..220..238C