Angular distributions in pion-nucleon Drell-Yan process

We study the Drell-Yan process in the polarized pion-nucleon scattering. We calculate the $U(1{)}_{\text{em}}$ gauge invariant hadron tensors. To this end, we have to take into account two diagrams—the standard diagram and an additional one—both diagrams are required to get the gauge invariant hadron tensor. We obtain a new single transverse spin asymmetry that probes gluon poles and chiral-odd distribution functions. The process of pion-nucleon scattering in the limit of large Feynman $x$ is described by a convolution of two non-collinear exclusive-channel distribution amplitudes, which demonstrates the duality between different factorization regimes.