Illuminating Light: Neutral meson production and direct photon correlations from small to large collision systems at the LHC

In an ultra relativistic collision between two heavy nuclei the temperature of the matter in the overlap region gets so large that a phase transition occurs between normal hadronic matter and a deconfined strongly coupled medium that we call the quark gluon plasma. In my thesis, this state of matter is studied using data from the ALICE detector at the LHC, using photons as the main experimental probe. My work pushed the photon reconstruction capabilities of the detector to its limits, measuring neutral mesons and direct photons with increased momentum range and precision. This allows us to learn more about particle production mechanisms even in the non-perturbative regime across all system sizes. Furthermore, there is a hint of a direct photon puzzle at the LHC.