Fig. 2.
(a) A model of the reaction where a circularly polarized virtual photon strikes an oppositely polarized up quark inside the proton. The spin of this quark flips and the quark recoils from its neighbours. A strange-antistrange quark pair is created from a Jπ = 0– two-gluon exchange (in lowest order) to produce the final state K+ and Λ hyperon. (b) A model of the reaction where an ss̅ quark pair is produced from a circularly polarized real photon that hadronizes such that the s quark in the Λ retains its full polarization after being "precessed" by a spin–orbit interaction, while the s̅ quark ends up in the spinless kaon. In both pictures the shaded band represents a spinless ud di-quark system.