Instanton induced transverse single spin asymmetry for $\pi^0$ production in $pp$-scattering

TL;DR

This paper models the transverse single-spin asymmetry in pion production during proton-proton collisions using instanton-induced interactions, successfully matching unpolarized cross sections and capturing the asymmetry's growth with transverse momentum.

Contribution

It introduces a novel calculation of spin asymmetry based on instanton effects without relying on fragmentation functions, aligning with experimental data.

Findings

Asymmetry reaches about 10% at high transverse momentum.

Unpolarized cross sections are consistent with experimental data.

Asymmetry increases with pion transverse momentum, matching observed trends.

Abstract

We calculate the production cross-section and the transverse single-spin asymmetry for pion in $p^{\uparrow}+p\to \pi^0 + X$. Our computation is based on existence of the instanton induced effective quark-gluon and quark-gluon-pion interactions with a strong spin dependency. In this framework we calculate the cross section without using fragmentation functions. We compare predictions of the model with data from RHIC. Our numerical results, based on the instanton liquid model for QCD vacuum, are in agreement with unpolarized cross section data. The asymmetry grows with the transverse momentum of pion $k_t$ in accordance with experimental observations. It reach value $\sim 10\%$ but at higher $k_t$ than experiment shows.