Constraining gluon poles

I.V Anikin,O.V Teryaev

doi:10.1016/j.physletb.2015.10.088

Abstract

In this letter, we revise the QED gauge invariance for the hadron tensor of Drell–Yan type processes with the transversely polarized hadron. We perform our analysis within the Feynman gauge for gluons and make a comparison with the results obtained within the light-cone gauge. We demonstrate that QED gauge invariance leads, first, to the need of a non-standard diagram and, second, to the absence of gluon poles in the correlators 〈ψ¯γ⊥A+ψ〉 related traditionally to dT(x,x)/dx. As a result, these terms disappear from the final QED gauge invariant hadron tensor. We also verify the absence of such poles by analyzing the corresponding light-cone Dirac algebra.

Highlights

KINEMATICSWe have observed the renaissance in the nucleon structure studies through the Drell-Yan type processes in the existing (FermiLab, Relativistic Heavy Ion Collider, see [1, 2]) and future (J-Parc, NICA) experiments
We have found that there is a contribution from the non-standard diagram which produces the imaginary phase required to have the single spin asymmetry (SSA)
We find that the QED gauge invariance can be maintained only by taking into account the non-standard diagram

Summary

KINEMATICS

We have observed the renaissance in the nucleon structure studies through the Drell-Yan type processes in the existing (FermiLab, Relativistic Heavy Ion Collider, see [1, 2]) and future (J-Parc, NICA) experiments. This additional contribution leads to an extra factor of 2 for the asymmetry. This conclusion was supported by analysis of the QED gauge invariance of the hadron tensor. The results in the Feynman and contour gauges coincide if the gluon poles in the correlators ψγ⊥A+ψ are absent This is in agreement with the relation between gluon poles and the Sivers function which corresponds to the "leading twist" Dirac matrix γ+. We study the hadron tensor which contributes to the single spin (left-right) asymmetry measured in the Drell-Yan process with the transversely polarized nucleon (see Fig. 1):.

THE DY HADRON TENSOR

QED GAUGE INVARIANCE OF HADRON TENSOR

CONCLUSIONS AND DISCUSSIONS