Direct photons in Au+Au collisions measured with the PHENIX detector at RHIC

TL;DR

This paper discusses measuring direct photons in Au+Au collisions at RHIC using the PHENIX detector, highlighting techniques to distinguish thermal radiation from other sources across different momentum ranges.

Contribution

It introduces methods for measuring low momentum direct photons via external conversion, enhancing understanding of quark-gluon plasma properties.

Findings

Successful measurement of low momentum direct photons

Identification of different photon sources by transverse momentum

Insights into thermal radiation from QGP and hadron gas

Abstract

A major goal of experiments in heavy-ion physics is the characterization of the quark gluon plasma (QGP) produced in the collision of heavy ions at high energy. Direct photons are a particularly good probe of the produced medium because they do not interact strongly and so can escape the medium unmodified, carrying information about when the photon was produced. It is expected that direct photon contributions from different sources (QGP radiation, hard scattering, hadron gas radiation) dominate at different transverse momentum ranges. Low momentum direct photons are dominated by thermal radiation (both from the QGP and hadron gas), while high momentum direct photons dominantly come from hard parton scatterings in the initial collision. We present a summary of techniques to measure direct photons with the PHENIX detector, with a focus on low momentum direct photons through their external conversion to dilepton pairs.