Twist-three Fragmentation Function Contribution to the Single Spin Asymmetry in pp Collisions

TL;DR

This paper investigates how twist-three fragmentation functions influence single spin asymmetries in proton-proton collisions, estimating their impact on pi0 production and explaining observed experimental differences.

Contribution

It provides the first estimate of the twist-three fragmentation function's contribution to single spin asymmetries in pp collisions, highlighting its significance.

Findings

The contribution is sizable and potentially explains the large asymmetry difference between eta and pi0 production.

The derivative contribution dominates the asymmetry in the forward region of the polarized proton.

Results suggest twist-three fragmentation functions are crucial for understanding spin asymmetries at RHIC.

Abstract

We study the twist-three fragmentation function contribution to the single transverse spin asymmetries in inclusive hadron production in pp collisions, pp->h+X. In particular, we evaluate the so-called derivative contribution which dominates the spin asymmetry in the forward direction of the polarized proton. With certain parametrizations for the twist-three fragmentation function, we estimate its contribution to the asymmetry of pi0 production at RHIC energy. We find that the contribution is sizable and might be responsible for the big difference between the asymmetries in eta and pi0 productions observed by the STAR collaboration at RHIC.