Single spin asymmetry in forward $pA$ collisions from Pomeron-Odderon interference

TL;DR

This paper proposes a new mechanism for transverse single spin asymmetry in high energy proton-nucleus collisions, based on Pomeron-Odderon interference, with potential experimental signatures and nuclear dependence.

Contribution

It introduces a novel contribution to SSA from Pomeron-Odderon interference in the dense nuclear target, including a complete formula and numerical estimates.

Findings

A_N can reach percent level in forward, low-P_h⊥ region

A_N exhibits significant suppression with increasing nuclear size

A node in A_N as a function of P_h⊥ could serve as an experimental test

Abstract

Working in the hybrid framework of the high energy $pA$ collisions we identify a new contribution to transverse single spin asymmetry (SSA). The phase necessary for the SSA is provided by the Pomeron-Odderon interference in the dense nuclear target. The complete formula for the $pA \to h X$ polarized cross section also contains the transversity distribution for the polarized projectile as well as the real part of the twist-3 fragmentation function. We numerically estimate the asymmetry $A_N$ and its nuclear dependence. Based on a model computation we find that $A_N$ can be a percent level in the forward and low-$P_{h\perp}$ region. For large nuclei we find significant suppression, with $A_N \propto A^{-7/6}$ parametrically. As a notable feature we find a node of $A_N$ as a function of the $P_{h\perp}$ around the values of the initial saturation scale that could be used to test this mechanism experimentally.