Exploration of jet energy loss via direct $\gamma$-charged particle azimuthal correlation measurements

TL;DR

This study measures azimuthal correlations of charged particles with direct photons and π0 in various collision systems at 200 GeV to investigate jet energy loss, revealing consistent suppression patterns across systems and with theoretical models.

Contribution

It provides new measurements of charged particle correlations with direct photons and π0 in heavy-ion and proton collisions, enhancing understanding of jet quenching mechanisms.

Findings

Suppression of associated yields in Au+Au collisions is similar to p+p and d+Au.

Associated yield suppression is constant across the measured photon energy fraction z_T.

Data align with theoretical predictions of jet energy loss models.

Abstract

The multiplicities of charged particles azimuthally associated with direct photons and $\pi^{0}$ have been measured for Au+Au, p+p, and d+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV in the STAR experiment. Charged particles with transverse momentum 0.5 $<$ $p_T^{h^{\pm}}$ $<$ 16 GeV/c for p+p and d+Au, and 3 $<$ $p_T^{h^{\pm}}$ $<$ 16 GeV/c for Au+Au and pseudorapidity $\mid\eta\mid$ $\leq$ 1.5 in coincidence with direct photons and $\pi^{0}$ of high transverse momentum 8 $<$ $p_T^{\gamma,\pi^{0}}$ $<$ 16 GeV/c at $\mid\eta\mid$ $\leq$ 0.9 have been used for this analysis. Within the considered range of kinematics, the observed suppressions of the associated yields per direct $\gamma$ in central Au+Au relative to p+p and d+Au are similar and constant with direct photon fractional energy $z_{T}$ ($z_{T}=p_{T}^{h^{\pm}}/p_{T}^{\gamma}$). The measured suppressions of the associated yields with direct $\gamma$ are comparable to those with $\pi^{0}$. The data are compared to theoretical predictions.