Double Sivers effect asymmetries and their impact on transversity measurements at RHIC

TL;DR

This paper investigates how double Sivers effect asymmetries influence transversity measurements at RHIC, emphasizing the importance of TMD effects as potential backgrounds in Drell-Yan processes.

Contribution

It provides a detailed estimate of TMD effects on double transverse spin asymmetries and suggests cross check measurements to constrain these backgrounds.

Findings

TMD effects can significantly contribute to observed asymmetries.

Cross check asymmetry measurements can help bound TMD background contributions.

Transverse momentum integrated asymmetries are less affected by TMD backgrounds.

Abstract

We study double transverse spin asymmetries in the Drell-Yan process at measured transverse momentum of the lepton pair. Contrary to what a collinear factorization approach would suggest, a nonzero double transverse spin asymmetry in the laboratory frame a priori does not imply nonzero transversity. TMD effects, such as the double Sivers effect, in principle form a background. Using the current knowledge of the relevant TMDs we estimate their contribution in the laboratory frame for Drell-Yan and W production at RHIC and point out a cross check asymmetry measurement to bound the TMD contributions. We also comment on the transverse momentum integrated asymmetries that only receive power suppressed background contributions.