Transverse single spin asymmetry in direct photon production in polarized pA collisions

TL;DR

This paper investigates the transverse single spin asymmetry in direct photon production during polarized proton-nucleus collisions, using a hybrid theoretical approach to explore color entanglement effects.

Contribution

It introduces a hybrid framework combining CGC and collinear twist-3 formalisms to analyze spin asymmetries and identifies a new, calculable color entanglement term affecting the cross section.

Findings

Discovery of an additional color entanglement term in the spin-dependent cross section.

Quantitative analysis of color entanglement effects on asymmetry.

Framework enables perturbative calculation of previously elusive contributions.

Abstract

We study the transverse single spin asymmetry in direct photon production in pA collisions with incoming protons being transversely polarized. To facilitate the calculation, we formulate a hybrid approach in which the nucleus is treated in the Color Glass Condensate (CGC) framework while the collinear twist-3 formalism is applied on the proton side. It has been found that an additional term which arises from color entanglement shows up in the spin dependent differential cross section. The fact that this additional term is perturbatively calculable allows us to quantitatively study color entanglement effects.