Soft-fermion-pole contribution to single-spin asymmetry for pion production in pp collisions

TL;DR

This paper investigates the role of soft-fermion-pole contributions within the twist-3 mechanism in collinear factorization, revealing their potential to significantly influence single-spin asymmetries in pion production during proton-proton collisions.

Contribution

It derives the SFP contribution to the twist-3 single-spin-dependent cross section, highlighting its potential large impact on asymmetries similar to the SGP contribution.

Findings

SFP can produce large asymmetries due to significant partonic cross sections.

SFP effects are comparable to SGP effects if the SFP function has similar magnitude.

Absence of derivative term for SFP distinguishes it from SGP contributions.

Abstract

We study the single transverse spin asymmetry for the inclusive pion production in the nucleon-nucleon collision, p^\uparrow p\to\pi X, based on the twist-3 mechanism in the collinear factorization. We derive the soft-fermion-pole (SFP) contribution to the twist-3 single-spin-dependent cross section associated with the twist-3 quark-gluon correlation functions in the polarized nucleon. We find that the SFP can give rise to a large effect to the asymmetry A_N owing to the large partonic hard cross sections with the large color factor, if the SFP function has a similar magnitude as the soft-gluon-pole (SGP) function, in spite of the absence of the "derivative term" for the SFP function unlike for the SGP function.