Prehydrodynamic evolution in large and small systems

We extend our previous investigation of the effects of prehydrodynamic evolution on final-state observables in heavy-ion collisions [38] to smaller systems. We use a state-of-the-art hybrid model for the numerical simulations with optimal parameters obtained from a previous Bayesian study. By studying p-Pb collisions, we find that the effects due to the assumption of a conformal evolution in the prehydrodynamical stage are even more important in small systems. We also show that this effect depends on the time duration of the pre-equilibrium stage, which is further enhanced in small systems. Finally, we show that the recent proposal of a free-streaming with subluminal velocity for the pre-equilibrium stage, thus effectively breaking conformal invariance, can alleviate the contamination of final-state observables. Our study further reinforces the need for moving beyond conformal approaches in pre-equilibrium dynamics modeling, especially when extracting transport coefficients from hybrid models in the high-precision era of heavy-ion collisions.

Automated summary

By studying p-Pb collisions, this study finds that the effects of assuming a conformal evolution in the prehydrodynamical stage are even more important in smaller systems. The study also shows that this effect is dependent on the time duration of the pre-equilibrium stage, which is further enhanced in small systems. Additionally, the study demonstrates that a free-streaming assumption with subluminal velocity for the pre-equilibrium stage can alleviate the contamination of final-state observables.