Single spin asymmetry in high energy QCD

TL;DR

This paper introduces a model integrating transverse spin asymmetries into high energy QCD saturation formalism, predicting specific behaviors of asymmetries in different collision scenarios and comparing qualitatively with experimental data.

Contribution

It presents a novel approach to incorporate T-odd effects into the saturation formalism using odderon exchange, advancing understanding of spin asymmetries in high energy QCD.

Findings

STSA increases with projectile x_F

STSA is non-monotonic in transverse momentum k_T

STSA in proton-nucleus collisions is smaller than in proton-proton collisions

Abstract

We present the first steps in an effort to incorporate the physics of transverse spin asymmetries into the saturation formalism of high energy QCD. We consider a simple model in which a transversely polarized quark scatters on a proton or nuclear target. Using the light-cone perturbation theory the hadron production cross section can be written as a convolution of the light-cone wave function squared and the interaction with the target. To generate the single transverse spin asymmetry (STSA) either the wave function squared or the interaction with the target has to be T-odd. In this work we use the lowest-order q->qG wave function squared, which is T-even, generating the STSA from the T-odd interaction with the target mediated by an odderon exchange. We study the properties of the obtained STSA, some of which are in qualitative agreement with experiment: STSA increases with increasing projectile x_F and is a non-monotonic function of the transverse momentum k_T. Our mechanism predicts that the quark STSA in polarized proton--nucleus collisions should be much smaller than in polarized proton--proton collisions. We also observe that the STSA for prompt photons due to our mechanism is zero within the accuracy of the approximation.