Gauge invariance, gluonic poles and single spin asymmetry in Drell-Yan processes

TL;DR

This paper investigates how gauge invariance and gluonic poles influence single spin asymmetries in Drell-Yan processes, revealing an enhancement factor of two due to additional contributions related to causality and contour gauge choices.

Contribution

It demonstrates the impact of contour gauge and gluonic pole prescriptions on gauge invariance and spin asymmetry calculations in Drell-Yan processes, highlighting a doubling of the asymmetry.

Findings

Single spin asymmetry is enhanced by a factor of two.

Gluonic pole prescriptions are linked to causality and contour gauge.

Extra contributions without an imaginary phase are identified.

Abstract

We explore the electromagnetic gauge invariance of the hadron tensor of the Drell-Yan process with one transversely polarized hadron. The special role is played by the contour gauge for gluon fields. The prescription for the gluonic pole in the twist 3 correlator is related to causality property and compared with the prescriptions for exclusive hard processes. As a result we get the extra contributions, which naively do not have an imaginary phase. The single spin asymmetry for the Drell-Yan process is accordingly enhanced by the factor of two.