On the odderon mechanism for transverse single spin asymmetry in the Wandzura-Wilczek approximation

TL;DR

This paper investigates the odderon mechanism's role in transverse single spin asymmetry in proton-proton and proton-nucleus collisions, finding it contributes zero at next-to-leading order under the Wandzura-Wilczek approximation.

Contribution

It identifies the relevant twist-3 distribution for the polarized proton and shows the odderon contribution vanishes at NLO in the Wandzura-Wilczek approximation.

Findings

Odderon contribution to asymmetry is zero at NLO under Wandzura-Wilczek approximation.

The intrinsic twist-3 PDF g_T(x) is key in the polarized cross section.

Additional twist-3 PDFs are relevant beyond the Wandzura-Wilczek approximation.

Abstract

We compute the transverse single spin asymmetry in forward $p^\uparrow p \to hX$ and $p^\uparrow A \to hX$ collisions from the odderon mechanism originally suggested by Kovchegov and Sievert [1]. Working in the hybrid approach of the Color Glass Condensate effective theory we firstly identify the relevant collinear parton distribution function (PDF) of the transversely polarized proton $p^\uparrow$ as the intrinsic twist-3 $g_T(x)$ distribution. We further argue that the complete polarized cross section also contains contributions from the kinematical and the dynamical twist-3 PDFs, in addition to the intrinsic twist-3 PDF. By restricting to the Wandzura-Wilczek approximation, where the dynamical twist-3 PDFs are dropped, we find that the odderon contribution to the polarized cross section for inclusive hadron production is exactly zero at the next-to-leading order in the strong coupling.