Physical Society Colloquium

The surprisingly strong strong interaction

Brian Cole

Department of Physics
Columbia University

The fundamental strong interaction is responsible for confining quarks inside protons and neutrons, and for binding protons and neutrons into atomic nuclei. More than 30 years ago it was predicted that ultra-high energy collisions between nuclei could produce a state of matter called quark-gluon plasma in which the quarks and the gluons, the exchange bosons of the strong interaction, would be deconfined. In this phase of matter, which could exist only at temperatures in excess of 10¹² Kelvin, it was thought that the intrinsic properties of the strong interaction might be more readily apparent.

In the last decade and a half, experiments at the Relativistic Heavy Ion Collider facility in the United States and the Large Hadron Collider (LHC) at CERN have provided compelling evidence that the quark gluon plasma is indeed being created in high-energy nuclear collisions. Furthermore, the interactions between the quark and gluon constituents of the plasma are found to be surprisingly strong. Recent measurements in proton-nucleus and, even, proton-proton collisions have shown similar strong-coupling dynamics as that observed in the nuclear collisions. Primarily relying on data from the ATLAS experiment at the LHC I will discuss our current understanding of the surprisingly strong strong interaction.