Heavy-quarkonium production in single-transverse-polarized high-energy scattering

We formulate the single transverse spin asymmetry in heavy quarkonium production in lepton-nucleon and nucleon-nucleon collisions in the nonrelativistic limit. We find that the asymmetry is very sensitive to the production mechanism. The final state interactions with the heavy quark and antiquark cancel out among themselves when the pair are produced in a color-singlet configuration, or cancel out with the initial state interaction in pp scattering when they are in color-octet. As a consequence, the asymmetry is nonzero in ep collisions only in the color-octet model, whereas in pp collisions only in the color-singlet model.