# Quark Matter 2014 - XXIV International Conference on Ultrarelativistic Nucleus-Nucleus Collisions

19-24 May 2014
Europe/Zurich timezone

## Centrality dependence of soft photon production and its collective flow in Au$+$Au collisions at $\sqrt{s_{NN}} = 200$ GeV

19 May 2014, 14:20
20m

### helium

Contributed Talk Collective Dynamics

### Speaker

Sanshiro Mizuno (University of Tsukuba (JP))

### Description

Soft photons are of particular interest since they are unmodified once produced, and thus carry information about the space-time thermal properties of the medium. We present new results on the centrality dependence of soft single photons in Au$+$Au collisions, down to $p_T = 400$ MeV/$c$ via photon conversions to $e^+e^-$ pairs. These measurements provide stringent tests of the hydrodynamic space-time evolution as a detailed function of the collision geometry. These soft photons have different angular emission patterns depending on their production mechanism. Previous published PHENIX results indicate that the second order Fourier coefficient ($v_2$) is postive for $p_T < 4$ GeV/$c$, which is qualitatively explained by hydrodynamical model calculations, but not quantitatively. The 3\textsuperscript{rd} order Fourier coefficient ($v_3$) of photons has been proposed as a critical additional handle to understand the photon emission. Photons emitted under the presence of strong magnetic field created in the collision would have a significant influence on $v_2$ while very little on $v_3$. In contrast, hydrodynamical models predict a sizable photon $v_3$. We report the latest results on the centrality dependence of the soft photon production and the $v_2$ and $v_3$ coefficients in Au$+$Au collisions at $\sqrt{s_{NN}} = 200$ GeV.
On behalf of collaboration: PHENIX

### Primary author

Sanshiro Mizuno (University of Tsukuba (JP))

 Slides