Anisotropy of low energy direct photons in relativistic heavy ion collisions

Using the Wigner function approach for electromagnetic radiation fields, we investigate the behavior of low energy photons radiated by the deceleration processes of two colliding nuclei in relativistic heavy ion collisions. The angular distribution reveals information of the initial geometric configurations, which is reflected in the anisotropic parameter v(2), with an increasing v(2) as energy decreases. This behavior is qualitatively different to the v(2) from the hadrons produced in the collisions.