Direct photon production in pp, p–Pb and Pb–Pb collisions measured with the ALICE experiment

We review recent ALICE results on direct photon production in pp, p–Pb and Pb–Pb collisions at LHC energies. In light systems, pp and p–Pb, no signal of direct photons at low $p_T$ < 3-5 GeV/$c$ is observed within uncertainties, while at high $p_T$ our measurements are consistent with NLO pQCD calculations. In central and mid-central Pb–Pb collisions a thermal photon contribution is observed at low $p_T$ < 3 - 4 GeV/$c$ with slopes $T_{eff}$ = (304 ± 11$^{stat}$ ± 40$^{syst}$) MeV and (407 ± 61$^{stat}$ ± 96$^{syst}$) MeV respectively. A collective elliptic flow of direct photons is measured and appeared to be close to the decay photon flow.