Hard- and soft-fermion-pole contributions to single transverse-spin   asymmetry for Drell-Yan process
  We study the single transverse-spin asymmetry for the Drell-Yan lepton pair production based on the twist-3 mechanism in the collinear factorization. We calculate all the hard-pole (HP) and the soft-fermion-pole (SFP) contributions to the single-spin-dependent cross section originating from the quark-gluon correlation functions in the transversely polarized nucleon in the leading order with respect to the QCD coupling constant. Combined with the soft-gluon-pole (SGP) contribution, this completes the corresponding twist-3 cross section. In the real photon limit, where all the HP contributions are transformed into the SFP contribution, we find that the SFP partonic hard cross section for the two independent quark-gluon correlation functions coincides in each scattering channel, as in the case of the inclusive light-hadron production. Our result enables one to extract the quark-gluon correlation functions from the forthcoming experiments at several facilities such as RHIC and J-PARC. 
Koichi Kanazawa and Yuji Koike
hep-ph