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 $A_{N}d\sigma (h{p}_{\uparrow }\to \mathrm{jet}+x)$, $A_{N}d\sigma (h{p}_{\uparrow }\to ``\pi \text{'}\text{'}x)$, where $p_{\uparrow }$ denotes a transversely polarized proton and "$\pi$" represents any spinless meson composed of light quarks. This approach provides testable relationships between different asymmetries.

• Received 28 April 1989

DOI:https://doi.org/10.1103/PhysRevD.41.83