Title: Heavy Ion Physics with Small Systems – Creating Droplets of the Early Universe

Abstract: A few microseconds after the big bang, the universe was in a phase of matter known as quark-gluon plasma (QGP). The goal of heavy-ion physics is to create, identify, and study the properties of the QGP using collisions of large nuclei at relativistic energies. One of the key results of this research is the finding that the QGP created in heavy-ion collisions is very well-described by viscous hydrodynamics. So-called small systems, those of a small projectile nucleus on a large target nucleus, have been used as a control experiment to help disentangle effects due to the QGP from effects due to the presence of a nucleus. Recent measurements, however, have indicated that small systems exhibit many of the same signatures believed to indicate the presence of the QGP in large systems. In this colloquium, we will discuss the latest experimental results and consider the implications for various theoretical scenarios.