Angular distributions in pion-nucleon Drell-Yan process

TL;DR

This paper investigates the polarized pion-nucleon Drell-Yan process, calculating gauge-invariant hadron tensors and revealing a new single transverse spin asymmetry linked to gluon poles and chiral-odd distributions.

Contribution

It introduces a comprehensive calculation of gauge-invariant hadron tensors including an additional diagram, and uncovers a novel spin asymmetry related to gluon poles in pion-nucleon scattering.

Findings

New single transverse spin asymmetry discovered

Gauge invariance achieved with two diagrams

Duality between factorization regimes demonstrated

Abstract

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.