The Evolution of Jets as Probes of the Quark Gluon Plasma, talk given by Dr. Rossi Reed of Lehigh University

The nuclear strong force, known as quantum chromodynamics (QCD), is one of the least understood of the four fundamental forces of nature as it cannot be understood via a perturbative expansion.  The collision of heavy-ions accelerated to ultrarelativistic speeds creates a droplet of matter so hot that the constituent protons and neutrons melt into quarks and gluons, which are collectively called partons.  This medium, called the quark gluon plasma (QGP), has an extremely low viscosity over entropy ratio, making it a nearly perfect liquid.  It is well established that the degrees of freedom of the plasma are partonic, rather than hadronic.  How this emergent property of QCD occurs is one of the fundamental questions of the field of high-energy nuclear physics.  In order to explain this property, an understanding of the structure of the plasma that it created is required, namely whether quasi-particles exist and if so, what is their extent.  To answer this, a probe with an extremeley small spatial resolution is required, and one such probe is particle jets created from high momentum transferred parton-parton collisions.  These collisions occur early in the heavy-ion collision dynamics, so that the high momentum partons created in these scatterings traverse the newly formed medium.  Understanding how these partons interact with the QGP provides critical insight into quantum chromodynamics.  In this talk, I will provide a general overview of the status and interpretation as well as future prospects for measuring jets in ultrarelativistic heavy ion collisions.  The existing measurements have reached new levels of precision and systematic control in recent years, with a wealth of new observables based on jet structure.  I will discuss what these measurements divulge about the nature of the QGP at both RHIC and the LHC, and give some insight on future prospects.