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{r arrow}2 scattering provide the leading contribution at large transverse momentum to asymmetries of the type {ital A}{sub {ital N}}d{sigma}(hp{sub {up arrow}}{r arrow}jet+{ital x}), {ital A}{sub {ital N}}d{sigma}(hp{sub {up arrow}}{r arrow} {pi}''x), where {ital p}{sub {up arrow}} denotes a transversely polarized proton and {pi}'' represents any spinless meson composed of light quarks. This approach provides testable relationships between different asymmetries.