Direct Photons and Photon-Hadron Correlations at PHENIX

TL;DR

This paper discusses measurements of direct photons at PHENIX in heavy-ion collisions, highlighting their role in probing the quark-gluon plasma's properties and the medium's thermalization and energy loss mechanisms.

Contribution

It presents new experimental measurements of direct photons across various collision systems, energies, and transverse momenta, advancing understanding of QGP characteristics.

Findings

Direct photons provide insights into the temperature of the quark-gluon plasma.

Photon-hadron correlations help study parton energy loss in the medium.

Azimuthal anisotropy of photons informs about medium thermalization.

Abstract

Direct photons are a powerful tool to study the hot and dense matter created in heavy-ion collisions at RHIC, since they are created in the different stages of the collision. Since they do not interact via the strong force, they can travel through the hot and dense matter mostly unaffected. The PHENIX experiment has measured direct photons using different methods, over a broad range of transverse momentum (\pt), in different collision systems, and at different energies. These measurements help interpreting the measurement of hadrons as well as understanding the temperature of the created quark-gluon plasma (QGP). The azimuthal anisotropy of direct photons may shed light on the thermalization time of the medium. Using direct photons to tag jets is a crucial tool to understand the energy loss of scattered partons in the medium.