Gamma-Jet Tomography of Quark-Gluon Plasma in High-Energy Nuclear Collisions

TL;DR

This paper uses NLO pQCD to demonstrate how gamma-jet correlations can tomographically probe the quark-gluon plasma, revealing surface versus volume emission based on hadron suppression patterns at different momentum ratios.

Contribution

It introduces a NLO pQCD-based method to analyze gamma-jet suppression, providing a detailed tomographic picture of the quark-gluon plasma in heavy-ion collisions.

Findings

High $z_T$ hadrons are dominated by surface emission.

Low $z_T$ hadrons mainly originate from volume emission.

Centrality dependence varies with $z_T$ region.

Abstract

Within the next-to-leading order (NLO) perturbative QCD (pQCD) parton model, suppression of away-side hadron spectra associated with a high $p_{T}$ photon due to parton energy loss is shown to provide a complete tomographic picture of the dense matter formed in high-energy heavy-ion collisions at RHIC. Dictated by the shape of the $\gamma$-triggered jet spectrum in NLO pQCD, hadron spectra at large $z_T=p_T^{h}/p_T^{\gamma} \stackrel{>}{\sim} 1$ are more susceptible to parton energy loss and therefore are dominated by surface emission of $\gamma$-triggered jets, whereas small $z_{T}$ hadrons mainly come from fragmentation of jets with reduced energy from volume emission. These lead to different centrality dependence of the hadron suppression in different regions of $z_{T}$.