11th International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions

Thermal photons are vital tool to study Quark-Gluon Plasma The photon production rate from the plasma at some temperature T is proportional to the transverse spectral function ${\rho }_T(\omega =|\overrightarrow{k}|,\overrightarrow{k})$. One can calculate the photon production rate also from the difference between ${\rho }_T(\omega ,\overrightarrow{k})$ (transverse) and ${\rho }_L(\omega ,\overrightarrow{k})$ (longitudinal) correlator as ${\rho }_L$ vanishes at the light cone. The UV part of ${\rho }_T-{\rho }_L$ is suppressed; therefore, the corresponding Euclidean correlator receives most of its contribution from the IR part of ${\rho }_T-{\rho }_L$. We also calculate the T-L correlator on $N_f=2+1$ flavor HISQ configurations with $m_l=m_s/5$ at temperature ∼1.15$T_c$ and 1.3 $T_c$. We have used two ansätze of the spectral function, which are 1) Polynomial ansatz of the spectral function connected to the UV region compatible with OPE expansion and 2) Hydro-inspired spectral function. We have also used the Backus-Gilbert method to estimate the spectral function. We will compare the photon production rate estimated from all these different methods.