Thermodynamics of the QCD Equation of State Near Deconfinement and the Critical Point



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The strong nuclear force is one of the four fundamental forces of our universe, and it is responsible for the stability of the atomic nucleus, through its binding of protons and neutrons, as well as the existence of all the hadrons which have been discovered. The quantum field theory which describes this force is quantum chromodynamics (QCD), and the exploration of this theory—through various experiments, models, and theoretical tools—has unveiled a phase diagram which we are still working to understand. There are two main features of this phase diagram which are central to my dissertation. First, is the deconfinement phase transition, where hadrons are melted into the quark-gluon plasma (QGP) via a smooth crossover at low chemical potentials. This exotic phase of matter was created microseconds after the Big Bang and it eventually cooled down into the hadronic matter which surrounds us today. Second, is the search for a critical point (CP) on this phase diagram, as the smooth crossover is expected to become a first-order phase transition at higher chemical potentials.

In this dissertation I will outline my work of creating partial pressures which enable us to see the contributions from different hadron families (distinguished for the first time by all three conserved charges BSQ) to the full pressure given by lattice QCD, the state-of-the-art simulations by which QCD can be solved numerically. Each partial pressure exhibits non-monotonic behavior, the signature of the onset of deconfinement for that respective hadron family. In addition, I present an improved open-source code that produces families of equations of state (EoSs) which include a CP at a user-defined location along the transition line. The updated EoS adds constraints which are relevant to Heavy-Ion Collisions (HICs) where physicists routinely create and study the QGP. An EoS is a required input for hydrodynamic simulations which describe these collisions, and it can help guide experimentalists in their search for its location on the QCD phase diagram, since it enables us to study signatures of the CP. I will then use this critical effect to understand how the mapping of the 3D Ising model CP onto the QCD phase diagram affects the net-proton kurtosis.



Quantum Chromodynamics, QCD, QCD Phase Diagram, Deconfinement, Thermodynamics,


Portions of this document appear in: Karthein, J. M., D. Mroczek, A. R. Nava Acuna, J. Noronha-Hostler, P. Parotto, D. R. P. Price, and C. Ratti. "Strangeness-neutral equation of state for QCD with a critical point." The European Physical Journal Plus 136, no. 6 (2021): 1-15; and in: Mroczek, D., AR Nava Acuna, J. Noronha-Hostler, P. Parotto, C. Ratti, and M. A. Stephanov. "Quartic cumulant of baryon number in the presence of a QCD critical point." Physical Review C 103, no. 3 (2021): 034901.