What are the degrees of freedom in the partonic fluid at RHIC ?

TL;DR

RHIC data suggests a deconfined, strongly coupled partonic phase with complex hadronization mechanisms, challenging simple fragmentation models and indicating a need to revise our understanding of degrees of freedom during the quark-gluon plasma phase.

Contribution

The paper reviews experimental evidence from RHIC indicating new hadronization mechanisms and a strongly coupled deconfined phase, questioning traditional models of partonic degrees of freedom.

Findings

Evidence of multiple hadron production mechanisms at RHIC

Lack of flavor dependence in collective properties

Challenges to simple fragmentation and thermal models

Abstract

Recent RHIC data show evidence of multiple hadron production mechanisms in heavy ion collisions compared to simple fragmentation in vacuum. I will review the measurements of collective flow, high momentum quenching, and two particle angular correlations to show that neither thermal production nor string fragmentation can describe the abundances, the angular distributions or the kinematic properties of all hadrons produced at RHIC. The proposed new hadronization mechanisms not only serve as evidence for a deconfined partonic phase of matter, but also for strong coupling of the degrees of freedom in the deconfined phase. I will point out a surprising lack of flavor dependence in these properties at RHIC, though, which might have to lead to further revisions of our understanding of the relevant degrees of freedom in the partonic phase and during the hadronization process.