Ratio of photon anisotropic flow in relativistic heavy ion collisions

The elliptic and triangular flow parameters of direct photons are known to be dominated by thermal radiations. The nonthermal contributions dilute the photon anisotropic flow by adding extra weight factor in the vn calculation. The discrepancy between experimental photon anisotropic flow data and results from theoretical model calculations is not well understood even after significant developments in the model calculations as well as in the experimental analysis methods. We show that the ratio of photon vn can be a potential observable in this regard by minimizing the nonthermal contributions. We calculate the v2/v3 of photons as a function of pT from heavy ion collisions at the BNL Relativistic Heavy Ion Collider (RHIC) and compare the results with available experimental data. The ratio is found to be larger for peripheral collisions than for central collisions. However, the pT dependent behavior of the ratio is found to be different than the individual flow parameters. The ratio is found to be sensitive to the initial conditions of the model calculation at different pT regions compared to the individual anisotropic flow parameters. We show that the photon v1/v2 and v1/v3 along with the v2/v3 results may help us constrain the initial conditions in heavy ion collisions.