Single-spin production asymmetries from the hard scattering of pointlike constituents

When one takes into account the transverse momenta of the constituents in a polarized proton, there exists a kinematic, "trigger-bias," effect in the formulation of the QCD-based hard-scattering model which can lead to single-spin production asymmetries. It seems convenient to represent the coherent spin-orbit forces in a polarized proton by defining an asymmetry in the transverse-momentum distribution of the fundamental constituents. It may then be possible to organize the hard-scattering model so that the kinematic constraints of hard 2 {→} 2 scattering provide the leading contribution at large transverse momentum to asymmetries of the type ANdσ(hp_↑→jet+x), ANdσ(hp_↑→``π''x), where p_↑ denotes a transversely polarized proton and "π" represents any spinless meson composed of light quarks. This approach provides testable relationships between different asymmetries.