# Early thermalization at RHIC

## TL;DR

This paper demonstrates that hydrodynamics can accurately model RHIC data on hadron spectra and elliptic flow, indicating rapid thermalization in the quark-gluon plasma phase, but it struggles with two-particle correlation data.

## Contribution

It provides strong evidence for early thermalization at RHIC and highlights the limitations of hydrodynamics in describing HBT correlations, suggesting the need for improved freeze-out modeling.

## Key findings

- Hydrodynamics reproduces single-particle spectra and elliptic flow.
- Hydrodynamics fails to describe HBT correlation data.
- Prediction of azimuthal oscillations of HBT radii in noncentral collisions.

## Abstract

It is shown that recent RHIC data on hadron spectra and elliptic flow can be excellently reproduced within a hydrodynamic description of the collision dynamics, and that this provides strong evidence for rapid thermalization while the system is still in the quark-gluon plasma phase. But even though the hydrodynamic approach provides an impressive description of the single-particle momentum distributions, it fails to describe the two-particle momentum correlation (HBT) data for central Au+Au collisions at RHIC. We suggest that this is not likely to be repaired by further improvements in our understanding of the early collision stages, but probably requires a better modelling of the freeze-out process. We close with a prediction of the phases of the azimuthal oscillations of the HBT radii in noncentral collisions at RHIC.