Abstract Colloquium Ralf Rapp

Heavy-Flavor Transport in the Quark-Gluon Plasma

The microscopic properties of the strongly coupled quark-gluon plasma (QGP)
remain a topic of great current interest, in particular in the context of
high-energy collisions of heavy nuclei. Particles containing a heavy charm or
bottom quark have turned out to be particularly promising probes of the transport
properties of the QGP. From the theoretical side, the mass of the heavy quarks
provides a large energy scale that enables considerable simplifications to study
their in-medium interactions and hadronization mechanisms, and to evalulate the
emerging transport properties in the QGP. In particular, at low momentum charm
and bottom quarks exert Brownian motion that provides a unique access to their
coupling strength to the thermal medium.
After a brief introduction to the basic QCD force and its in-medium manifestations,
we discuss the main theoretical approaches that are being pursued to describe the
diffusion of heavy quarks in the QGP and their hadronization. Current phenomenological
applications to heavy-flavor data from the Relativistic Heavy-Ion Collider and the
Large Hadron Collider are still beset with significant uncertainties, but they already
indicate a clear need for a large nonperturbative interaction strength in the QGP
at moderate temperatures. We discuss how these uncertainties can be systematically
reduced. In particular, constraints from lattice-QCD data suggest that remnants of
the confining force play a key role in the understanding of the QGP as a strongly
coupled quantum liquid.