Light-heavy-ion collisions: a window into pre-equilibrium QCD dynamics?

Relativistic collisions of light on heavy ions (p + Au at GeV, p + Au , d + Au ,He + Au at GeV and 200 GeV and p + Pb ,He + Pb at 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 GeV is predicted to be similar in magnitude to that found in He + Au collisions. Furthermore, the ratio of He + 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.