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

19-24 May 2014
Europe/Zurich timezone

## QGP formation time and the elliptic flow of direct photons

20 May 2014, 16:30
2h

### spectrum

Board: G-20
Poster Electromagnetic Probes

### Speaker

Mrs Fu-Ming LIU (CCNU, Wuhan)

### Description

In this talk we investigate the information carried by the large elliptic flow of direct photons, observed at RHIC and LHC, in the frame work of (3+1)-dimensional ideal hydrodynamical model constrained with hadronic data. It is found that the transverse momentum spectra of direct photons can be explained much more easily, while a good explanation of the observed elliptic flow of direct photons can only be reached if the two time scales, thermal and chemical equilibrium are chosen properly, ie, about $1/3$~fm/c and 2~fm/c, respectively. The realization of thermal and chemical equilibrium are hot questions in relativistic heavy ion physics. The elliptic flow of direct photon serves as a more strict clock to those questions than other observables. High order harmonics of direct photons from PbPb collisions at 2.76~TeV are also predicted based on event-by-event fluctuation in this work, which look very similar to those of hadrons.
On behalf of collaboration: None

### Primary author

Mrs Fu-Ming LIU (CCNU, Wuhan)

 Poster