# On the elliptic flow of heavy quarkonia in $pA$ collisions

## TL;DR

This paper uses the Color Glass Condensate framework to analyze the elliptic flow of heavy quarkonia in proton-nucleus collisions, explaining recent experimental observations as an initial state effect and predicting similar flow for $mbda$ and $J/$ mesons.

## Contribution

It provides a theoretical interpretation of heavy-flavor elliptic flow in $pA$ collisions as an initial state effect within the CGC framework, and predicts similar flow for $mbda$ and $J/$ mesons.

## Key findings

- Heavy-flavor mesons have elliptic flow comparable to light hadrons.
- The observed flow can be explained by initial state interactions in the CGC framework.
- Predicted similar flow for $mbda$ and $J/$ mesons, testable in future experiments.

## Abstract

Using the dilute-dense factorization in the Color Glass Condensate framework, we investigate the azimuthal angular correlation between a heavy quarkonium and a charged light hadron in proton-nucleus collisions. We extract the second harmonic $v_2$, commonly known as the elliptic flow, with the light hadron as the reference. This particular azimuthal angular correlation between a heavy meson and a light hadron has first been measured at the LHC recently. The experimental results indicate that the elliptic flows for heavy-flavor mesons ($J/\psi$ and $D^0$) are almost as large as those for light hadrons. Our calculation demonstrates that this result can be naturally interpreted as an initial state effect due to the interaction between the incoming partons from the proton and the dense gluons inside the target nucleus. Since the heavy quarkonium $v_2$ exhibits a weak mass dependence according to our calculation, we predict that the heavy quarkonium $\Upsilon$ should have a similar elliptic flow as compared to that of the $J/\psi$, which can be tested in future measurements.