Quantum Transport and Hadronization in QCD Matter

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In the first few microseconds after the Big Bang, the Universe was filled with an extremely hot substance called quark-gluon plasma (QGP). It is fascinating that about 14 billion years later, the QGP can be recreated and studied in the laboratory by colliding atomic nuclei at very high energies. It is of fundamental interest to understand how the quarks and gluons transition into bound states called hadrons, such as protons and neutrons, which are the building blocks of the visible matter in the Universe and make up about 98% of its mass. However, due to the very short lifetime of the QGP in the laboratory, its properties have to be inferred from the thousands of particles that are observed in large detectors. Thus far, the observed particle spectra indicate that the QGP behaves like a very strongly coupled, near-perfect liquid whose transport properties are close to universal lower bounds set by quantum mechanics. In this project the PI, together with his team of graduate and undergraduate students, investigates how the properties of the QGP and its hadronization emerge from the fundamental theory of the strong nuclear force, Quantum Chromodynamics (QCD).A key property of the "strongly-coupled QGP" (sQGP) are very large interaction rates between its constituents. These interaction rates imply a very large quantum-mechanical uncertainty in the energies of the particles, and are conjectured to be closely related to the quantum lower bounds in the transport properties of the hot QCD medium. The PI employs rigorous quantum many-body theory to self-consistently calculate the spectral distributions and scattering amplitudes of the medium particles, both for quarks and gluons in the QGP and for the composite hadrons in the hadronic medium. He utilizes effective theories to constrain the fundamental interactions through information from first-principles lattice-QCD computations. In particular, he develops a framework that enables calculation of the transition from quarks and gluons to hadrons based on their in-medium spectral properties. His theoretical calculations are applied in transport models for heavy charm and bottom quarks, which allow for comparisons to, and interpretations of, experimental data from the Relativistic Heavy-Ion Collider at Brookhaven Lab and the Large Hadron Collider in Europe. His program fosters an inclusive scholarly environment including undergraduate research and outreach activities to regional high-school students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.