Tomography of high-energy nuclear collisions with photon-hadron correlations

TL;DR

This paper proposes a method to map the spatial distribution of jet quenching in quark-gluon plasma using photon-hadron correlations, providing a tomographic approach to study high-energy nuclear collisions.

Contribution

It introduces a NLO pQCD-based framework to analyze gamma-hadron suppression patterns and their dependence on collision centrality and orientation, enabling detailed tomography of the quark-gluon plasma.

Findings

High $z_T$ hadrons are surface-dominated, sensitive to jet energy loss.

Low $z_T$ hadrons originate from volume emission, less sensitive to surface effects.

Different suppression patterns depend on collision centrality and pair orientation.

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 studied in high-energy heavy-ion collisions. Dictated by the shape of the $\gamma$-associated jet spectrum in NLO pQCD, hadron spectra at large $z_T=p_T^{h}/p_T^{\gamma} \stackrel{>}{\sim} 1$ are more sensitive to parton energy loss and therefore are dominated by surface emission of $\gamma$-associated jets, whereas small $z_{T}$ hadrons mainly come from fragmentation of jets with reduced energy which is controlled by the volume emission. These lead to different centrality dependence of the $\gamma$-hadron suppression for different values of $z_{T}$. Therefore, a complete measurement of the suppression of $\gamma$-triggered hadron spectra, including its dependence on the orientation of the $\gamma$-hadron pair with respect to the reaction plane, allows the extraction of the spatial distribution of jet quenching parameters, achieving a true tomographic study of the quark-gluon plasma in high-energy heavy-ion collisions.