Probing the path-length dependence of parton energy loss via scaling properties in heavy ion collisions

TL;DR

This paper investigates how parton energy loss depends on the path length in quark-gluon plasma by analyzing suppression patterns and azimuthal anisotropy in heavy ion collisions, confirming a linear relationship consistent with pQCD predictions.

Contribution

It demonstrates a scaling property of parton energy loss with path length and relates azimuthal anisotropy to suppression, providing new methods to probe energy loss mechanisms.

Findings

Energy loss scales with path length as L^1.02

Azimuthal anisotropy follows the same scaling as suppression

Linear relationship between v2/e and the derivative of R_AA

Abstract

The scaling property of large-$p_\perp$ hadron suppression, $R_{\rm{AA}}(p_\perp)$, measured in heavy ion collisions at RHIC and LHC leads to the determination of the average parton energy loss $\langle \epsilon \rangle$ in quark-gluon plasma produced in a variety of collision systems and centrality classes. Relating $\langle \epsilon \rangle$ to the particle multiplicity and collision geometry allows for probing the dependence of parton energy loss on the path-length $L$. We find that $\langle \epsilon \rangle \propto L^\beta$ with $\beta=1.02^{+0.09}_{-0.06}$, consistent with the pQCD expectation of parton energy loss in a longitudinally expanding quark-gluon plasma. We then demonstrate that the azimuthal anisotropy coefficient divided by the collision eccentricity, $v_2/\textrm{e}$, follows the same scaling property as $R_{\rm{AA}}$. This scaling is observed in data, which are reproduced by the model at large $p_\perp$. Finally, a linear relationship between $v_2/\textrm{e}$ and the logarithmic derivative of $R_{\rm{AA}}$ is found and confirmed in data, offering an additional way to probe the $L$ dependence of parton energy loss using coming measurements from LHC Run 3.