Color gauge invariance in the Drell-Yan process

TL;DR

This paper examines the color gauge invariance of the Drell-Yan process, focusing on twist-three contributions and soft gluon poles, clarifying discrepancies in previous results for single spin asymmetries.

Contribution

It provides a gauge-invariant formulation of the Drell-Yan cross section at next-to-leading twist and resolves conflicting results regarding single spin asymmetries.

Findings

Gauge-invariant expression for the hadron tensor.

Clarification of the soft gluon pole treatment.

Resolution of discrepancies in spin asymmetry results.

Abstract

We consider the color gauge invariance of a factorized description of the Drell-Yan process cross section. In particular, we focus on the next-to-leading twist contributions for polarized scattering and on the cross section differential in the transverse momentum of the lepton pair in the region where the transverse momentum is small compared to the hard scale. The hadron tensor is expressed in terms of manifestly color gauge invariant, nonlocal operator matrix elements and a color gauge invariant treatment of soft gluon poles is given. Also, we clarify the discrepancy between two published results for a single spin asymmetry in the Drell-Yan cross section. This asymmetry arises if such a soft gluon pole is present in a specific twist-three hadronic matrix element.