Single spin asymmetry and five-quark components of the proton
  We examine the single-spin asymmetry (SSA) caused by the five-quark components of the proton for semi-inclusive electroproduction of charged pions in deep-inelastic scattering on a transversely polarized hydrogen target. The large SSA is considered to have close relation with quark orbital motion in the proton and suggests that the quark orbital angular momentum is nonzero. For the five-quark $qqqq\bar{q}$ components of the proton, the lowest configurations with $qqqq$ system orbitally excited and the $\bar{q}$ in the ground state would give spin-orbit correlations naturally for the quarks in a polarized proton. We show that based on the basic reaction $\gamma q \to \pi q'$, the orbital-spin coupling of the probed quarks in the five-quark configuration leads to the single-spin asymmetry consistent with recent experiment results. 
F.X.Wei and B.S.Zou