# Light-Heavy Ion Collisions: A window into pre-equilibrium QCD dynamics?

## TL;DR

This paper uses simulations to explore whether hydrodynamics can describe small light-heavy ion collision systems, revealing potential experimental signatures of pre-equilibrium QCD dynamics through flow measurements.

## Contribution

It demonstrates that hydrodynamic models can apply to small systems and predicts observable flow signatures sensitive to pre-equilibrium dynamics in light-heavy ion collisions.

## Key findings

- Triangular flow in d+Au at 200 GeV is comparable to 3He+Au.
- The v3(p_T) ratio between 3He+Au and d+Au is sensitive to pre-equilibrium flow.
- Hydrodynamics may describe systems with only a few tens of particles.

## Abstract

Relativistic collisions of light on heavy ions (p+Au at sqrt(s)=7.7 GeV, p+Au, d+Au,3He+Au at sqrt(s)=62.4 GeV and 200 GeV and p+Pb, 3He+Pb at sqrt(s)=5.02 TeV) are simulated using "superSONIC", a model that includes pre-equilibrium flow, viscous hydrodynamics and a hadronic cascade afterburner. Even though these systems have strong gradients and only consist of at most a few tens of charged particles per unit rapidity, one finds evidence that a hydrodynamic description applies to these systems. Based on these simulations, the presence of a triangular flow component in d+Au collisions at sqrt(s)=200 GeV is predicted to be similar in magnitude to that found in 3He+Au collisions. Furthermore, the v3(p_T) ratio of 3He+Au to d+Au is found to be sensitive to the presence of pre-equilibrium flow. This would imply an experimentally accessible window into pre-equilibrium QCD dynamics using light-heavy ion collisions.