PHENIX results on jet modification with $\pi^0$- and photon-triggered two particle correlations in $p$$+$$p$, $p(d)$+Au, and Au+Au collisions

TL;DR

This paper reports PHENIX measurements of jet modifications via $\pi^0$ and direct photon-triggered correlations across various collision systems, revealing no modification in small systems and detailed transition patterns in Au+Au collisions.

Contribution

It provides new experimental data on jet modifications and the transition from suppression to enhancement in heavy-ion collisions using photon and $\pi^0$ triggers.

Findings

No modification in $p$+Au and d+Au for direct photons.

Increased away-side width for $\pi^0$ in $p$+Au.

Transition from suppression to enhancement in Au+Au collisions.

Abstract

As a colorless probe, direct photons balance the $p_T$ of the away-side jet at leading order. Direct photon-hadron correlations are thus an excellent probe for nuclear structure and QCD effects, including parton energy loss in the Quark-Gluon Plasma. PHENIX has measured $\pi^{0}$ and direct photon-triggered two-particle azimuthal correlations in a variety of collision systems ranging from $p$$+$$p$ to Au+Au at 200 GeV. In $p$$+$Au and $d$$+$Au collisions, no modification of the per-trigger jet yield or away-side correlation width compared to $p$$+$$p$ collisions is observed for direct photon triggered correlations while an increase in the away-side width for $\pi^{0}$ triggered correlations in $p$$+$Au has been measured. In Au+Au collisions, direct photons have been identified statistically as well as using an isolation cut. Combining data sets from different collision systems allows us to quantify the transition from suppression at high $z_T$ $(p_{T,h}/p_{T,\gamma})$ to the enhancement of low $z_T$ particles relative to $p$$+$$p$, and to study this transition as a function of trigger $p_T$.