# Quark Matter 2018

13-19 May 2018
Venice, Italy
Europe/Zurich timezone
The organisers warmly thank all participants for such a lively QM2018! See you in China in 2019!

## Universal Scaling of Low Momentum Direct Photon Production in Relativistic Heavy Ion Collisions

15 May 2018, 17:00
2h 40m
First floor and third floor (Palazzo del Casinò)

### First floor and third floor

#### Palazzo del Casinò

Poster Electromagnetic and weak probes

### Description

Direct photons are an important tool with unique capabilities to study the colored medium created in (ultra)relativistic heavy ion collisions. We map out the low momentum direct photon observables and present the results of the measurements in Au+Au collisions at $\sqrt{s_{NN}} = 62.4$ GeV and $\sqrt{s_{NN}} = 39$ GeV, using data samples of externally converted photons. These results are aimed to further constrain the sources of the low momentum direct photons, in addition to the previous PHENIX measurement results at $\sqrt{s_{NN}} = 200$ GeV. The observed direct photon excess yield at these three collision energies can be interpreted as an evidence of thermal radiation from the Quark Gluon Plasma.

We have found that at low-$p_{T}$ the yield of direct photons, $dN_{\gamma}/dy$, from heavy ion collisions follows a universal scaling as a function of the charged-particle multiplicity $(dN_{ch}/d\eta)^{\alpha}$, where we combine the data from various collision systems at four center-of-mass energies. The prompt photon yield seems to have the similar functional behavior. The observed scaling properties of direct photons from these systems show that the strength of the thermal radiation source increases faster than the charged-particle multiplicity. In this poster we present these new results.

Centralised submission by Collaboration Presenter name already specified PHENIX Experiment

### Presentation Materials

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