Physical Review D
Using the covariant spectator theory, we present the results of a valence quark-diquark model calculation of the nucleon structure function f(x) measured in unpolarized deep inelastic scattering and the structure functions g(1)(x) and g(2)(x) measured in deep inelastic scattering using polarized beams and targets. Parameters of the wave functions are adjusted to fit all the data. The fit fixes both the shape of the wave functions and the relative strength of each component. Two solutions are found that fit f(x) and g(1)(x), but only one of these gives a good description of g(2)(x). This fit requires the nucleon covariant spectator theory wave functions contain a large D-wave component (about 35%) and a small P-wave component (about 0.6%). The significance of these results is discussed.
Gross, F., Ramalho, G., & Pena, M. T. (2012). Spin and angular momentum in the nucleon. Physical Review D, 85(9), 093006.