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

May 19, 2014, 2:20 PM
helium (darmstadtium)



Schlossgraben 1 64283 Darmstadt Germany
Contributed Talk Collective Dynamics Electromagnetic probes


Sanshiro Mizuno (University of Tsukuba (JP))


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))

Presentation materials