Quantifying Properties of the QCD Matter at RHIC

TL;DR

This paper reviews recent experimental results on the bulk properties of quark-gluon plasma at RHIC, focusing on parton energy loss, azimuthal anisotropy, and transverse momentum distributions, providing empirical constraints and insights into the medium's dynamics.

Contribution

It offers new empirical constraints on parton energy loss and its dependence on collision centrality and particle rapidity density at RHIC.

Findings

Constant fraction of parton energy loss (~25%) at high pT.

Energy loss fraction proportional to particle density over collision area.

Flat R_AA as a function of pT indicating uniform energy loss across high pT range.

Abstract

We will review recent results on quantitative description of global properties of bulk partonic matter at RHIC. These results include strangeness phase space factor of the partonic matter, azimuthal angular anisotropy $v_2$, and transverse momentum $p_T$ distributions of effective partons at the hadronization of bulk partonic matter. We present empirical constraints on parton energy loss in the high $p_T$ region ($>$ 5 GeV/c). A flat $R_{AA}$ as a function of $p_T$ at mid-rapidity implies a constant fraction of the parton energy loss ($\Delta p_T/p_T$) and the fraction reaches 25% for neutral $\pi$, charged hadrons and non-photonic electrons of heavy quark decays from central Au+Au collisions at $\sqrt{s_{NN}}$ 200 GeV. Collision centrality dependence of $\Delta p_T/p_T$ from Au+Au and Cu+Cu collisions indicates that the fraction is approximately proportional to particle rapidity density $dn/dy$ divided by the initial transverse overlapping area of the colliding nuclei. Implications on dynamics of parton energy loss will be discussed.