I retrace the developments from Hagedorns concept of a limiting temperature for hadronic matter to the discovery and characterization of the quark-gluon plasma as a new state of matter. My recollections begin with the transformation more than 30 year
s ago of Hagedorns original concept into its modern interpretation as the critical temperature separating the hadron gas and quark-gluon plasma phases of strongly interacting matter. This was followed by the realization that the QCD phase transformation could be studied experimentally in high-energy nuclear collisions. I describe here my personal effort to help develop the strangeness experimental signatures of quark and gluon deconfinement and recall how the experimental program proceeded soon to investigate this idea, at first at the SPS, then at RHIC, and finally at LHC. As it is often the case, the experiment finds more than theory predicts, and I highlight the discovery of the perfectly liquid quark-gluon plasma at RHIC. I conclude with an outline of future opportunities, especially the search for a critical point in the QCD phase diagram.
This lecture presents an overview of the status of the investigation of the properties of the quark-gluon plasma using relativistic heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). It focuses on
the insights that have been obtained by the comparison between experimental data from both facilities and theoretical calculations.
The Caldeira-Leggett model describes a microscopic quantum system, represented by a harmonic oscillator, in interaction with a heat bath, represented by a large number of harmonic oscillators with a range of frequencies. We consider the case when the
system oscillator starts out in the ground state and then thermalizes due to interactions with the heat bath, which is at temperature $theta$. We calculate the position autocorrelation function $<x(t)x(t)>$ of the system oscillator at two different times and study its behaviour in the small and large time limits. Our results show that the system oscillator thermalizes as expected. We also confirm by explicit calculation that the position autocorrelation function exhibits periodicity for imaginary values of the time difference $t-t = itau$ at late (real) times $t$.
This lecture presents a concise review of the current status of hard QCD and electromagnetic processes as probes of the quark-gluon plasma.
I review some aspects of the role of strange quarks in hot QCD matter and as probes of quark deconfinement at high temperature.
