Accessing tri-gluon correlations in the nucleon via the single spin asymmetry in open charm production

TL;DR

This paper calculates the single transverse-spin asymmetry in open charm production in proton-proton collisions, highlighting the significance of tri-gluon correlations as a probe for understanding the nucleon's internal spin structure.

Contribution

It introduces a method to access tri-gluon correlations through single spin asymmetries in open charm production, emphasizing their potential to reveal new insights into nucleon structure.

Findings

Quark-gluon correlations produce negligible asymmetry.

Tri-gluon correlations can cause significant asymmetry.

Asymmetry differences between D and anti-D mesons are notable.

Abstract

We calculate the single transverse-spin asymmetry for open charm production in $pp$ collisions within the QCD collinear factorization approach. We include contributions from both twist-three quark-gluon and tri-gluon correlation functions. We find that the quark-gluon correlation functions alone generate only a very small asymmetry for open charm production in the kinematic region of current interest at RHIC, so that the observation of any significant single-spin asymmetry would be a clear indication of the presence of tri-gluon correlations inside a polarized proton. We furthermore demonstrate that the tri-gluon contribution could be very different for the production of $D$ and $\bar{D}$ mesons. These features make the single spin asymmetry in open charm production in polarized $pp$ collisions at RHIC an excellent probe of tri-gluon correlation functions.