  In high-energy collisions of small systems, by high-enough final-state
multiplicities, a collective behaviour is present that is similar to the flow
patterns observed in heavy-ion collisions. Recent studies connect this
collectivity to semi-soft vacuum-QCD processes. Here we explore QCD production
mechanisms using angular correlations of heavy flavour using simulated
proton-proton collisions at $\sqrt{s} = 13$~TeV with the PYTHIA8 Monte Carlo
event generator. We demonstrate that the event shape is strongly connected to
the production mechanisms. Flattenicity, a novel event descriptor, can be used
to separate events containing the final-state radiation from the rest of the
events.

High Energy Physics - Phenomenology