Measurement of two-particle correlations with respect to second- and third-order event planes in Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV

TL;DR

This paper investigates two-particle azimuthal correlations in gold-gold collisions at 200 GeV, revealing modifications consistent with jet quenching and path-length-dependent energy loss, and explores their dependence on event-plane angles.

Contribution

It provides detailed measurements of azimuthal correlations with respect to second- and third-order event planes, including their shape, yield, and asymmetries, advancing understanding of jet quenching mechanisms.

Findings

Suppressed away-side yield at high trigger pT compared to p+p collisions.

Modified away-side shape and yield at low associated pT, consistent with radiative energy loss.

Observed asymmetry related to the second-order event plane, indicating path-length dependence.

Abstract

We present measurements of azimuthal correlations of charged hadron pairs in $\sqrt{s_{_{NN}}}=200$ GeV Au$+$Au collisions for the trigger and associated particle transverse-momentum ranges of $1<p_T^t<10$~GeV/$c$ and $0.5<p_T^a<10$~GeV/$c$. After subtraction of an underlying event using a model that includes higher-order azimuthal anisotropy $v_2$, $v_3$, and $v_4$, the away-side yield of the highest trigger-\pt ($p_T^t>4$~GeV/$c$) correlations is suppressed compared to that of correlations measured in $p$$+$$p$ collisions. At the lowest associated particle $p_T$ ($0.5<p_T^a<1$ GeV/$c$), the away-side shape and yield are modified relative to those in $p$$+$$p$ collisions. These observations are consistent with the scenario of radiative-jet energy loss. For the low-$p_T$ trigger correlations ($2<p_T^t<4$ GeV/$c$), a finite away-side yield exists and we explore the dependence of the shape of the away-side within the context of an underlying-event model. Correlations are also studied differentially versus event-plane angle $\Psi_2$ and $\Psi_3$. The angular correlations show an asymmetry when selecting the sign of the difference between the trigger-particle azimuthal angle and the $\Psi_2$ event plane. This asymmetry and the measured suppression of the pair yield out of plane is consistent with a path-length-dependent energy loss. No $\Psi_3$ dependence can be resolved within experimental uncertainties.