Within the Standard Model, the behaviour of matter at its fundamental scale is described by Quantum Chromodynamics (QCD). This theory formalises the strong interaction that exists between quarks and gluons, generically referred to as partons, and predicts their confinement within hadrons in normal temperature and density conditions. A very energetic context may lead to free the partons from their hadronic structure, resulting in a Quark-Gluon Plasma (QGP) predicted by the QCD theory and experimentally expected in ultrarelativistic heavy-ion collisions such as those provided by the lead-lead (Pb–Pb) system. The ALICE experiment (A Large Ion Collider Experiment) located at the CERN Large Hadron Collider (LHC) can observe such collisions as well as the proton-proton (pp) and proton-lead (p–Pb) systems for which the emergence of a QGP is not predicted, constituting therefore mandatory references to Pb–Pb studies.
In this presentation we are interested in direct photons produced at the earliest time of the collision in hard processes between partons, in the case of p–Pb collisions at √