Jet-like Correlations with Direct-Photon and Neutral-Pion Triggers at $\sqrt{s_{_{NN}}} = 200$ GeV

TL;DR

This study investigates jet-like correlations with direct-photon and neutral-pion triggers in heavy-ion and proton-proton collisions at 200 GeV, revealing suppression patterns and energy loss behaviors consistent with theoretical models.

Contribution

It provides new measurements of azimuthal correlations for direct-photon and neutral-pion triggers, comparing suppression effects in Au+Au and p+p collisions at 200 GeV.

Findings

Suppression of away-side yields is independent of trigger transverse momentum.

Similar suppression levels observed for photon and pion triggers as a function of z_T.

Energy loss manifests mainly as low transverse momentum particles.

Abstract

Azimuthal correlations of charged hadrons with direct-photon ($\gamma_{dir}$) and neutral-pion ($\pi^{0}$) trigger particles are analyzed in central Au+Au and minimum-bias $p+p$ collisions at $\sqrt{s_{_{NN}}} = 200$ GeV in the STAR experiment. The charged-hadron per-trigger yields at mid-rapidity from central Au+Au collisions are compared with $p+p$ collisions to quantify the suppression in Au+Au collisions. The suppression of the away-side associated-particle yields per $\gamma_{dir}$ trigger is independent of the transverse momentum of the trigger particle ($p_{T}^{\mathrm{trig}}$), whereas the suppression is smaller at low transverse momentum of the associated charged hadrons ($p_{T}^{\mathrm{assoc}}$). Within uncertainty, similar levels of suppression are observed for $\gamma_{dir}$ and $\pi^{0}$ triggers as a function of $z_{T}$ ($\equiv p_T^{\mathrm{assoc}}/p_T^{\mathrm{trig}}$). The results are compared with energy-loss-inspired theoretical model predictions. Our studies support previous conclusions that the lost energy reappears predominantly at low transverse momentum, regardless of the trigger energy.