Direct photon production and jet energy-loss in small systems

Understand

Two types of penetrating probes, direct photon and QCD jets, are investigated in the background of a small and rapidly expanding droplet of quark-gluon plasma.

• The additional thermal electromagnetic radiation results in a $\sim$50\% enhancement of the direct photons.
• In high multiplicity p+Pb collisions, jets can lose a sizeable fraction of their initial energy, leading to a charged hadron $R_\mathrm{pA}$ of $\sim$0.8 at a transverse momentum around 10\,GeV.
• Those two proposed measurements can help understand the apparent collective behaviour observed in small collision systems.