Heavy flavor collectivity in small systems

TL;DR

This paper reviews recent measurements of heavy flavor hadron flow and production in small collision systems, exploring whether observed correlations are due to initial-state effects or collective behavior similar to heavy ion collisions.

Contribution

It provides a comprehensive overview of recent experimental results on heavy flavor collectivity in small systems, highlighting their implications for understanding QCD effects and the origin of flow.

Findings

Heavy flavor hadrons show signs of collective flow in small systems.

Initial-state momentum correlations may contribute to azimuthal anisotropy.

Heavy quark probes help disentangle different QCD effects.

Abstract

The presence of correlations between particles significantly separated in pseudorapidity in proton-proton and proton-nucleus collisions revealed surprises in the early LHC data. Are the physical processes responsible for the observed long-range pseudorapidity correlations and their azimuthal structure the same in small collision systems as in heavy ion collisions? Whereas in the case of heavy ion collisions "flow" is interpreted as generated by initial geometric inhomogeneities, calculations indicate that initial-state momentum correlations are present and could contribute to the observed azimuthal anisotropy in small systems. Probes involving heavy quarks provide us with a unique opportunity to disentangle different quantum chromodynamics effects at the boundary between low- and high-$p_{\mathrm{T}}$ interactions, and hence shed light on the origin of flow in small collision systems. A selection of the latest measurements is presented for the flow and production of heavy flavor hadrons and their decay products.