Dissertation Defense: Saehanseul Oh, Yale University, “Correlations in particle production in proton-lead and lead-lead collisions at the LHC”

In high-energy heavy-ion collisions at the Large Hadron Collider (LHC), a hot and dense state of matter called the Quark-Gluon Plasma (QGP) is formed. The initial collision geometry and the subsequent expansion during the QGP stage result in the correlations of produced particles, through which the properties of the QGP can be investigated. Two analyses based on the geometrical correlations of produced particles, one in proton-lead (p–Pb) collisions and the other in lead-lead (Pb–Pb) collisions, are presented in this thesis. In the forward-central two-particle correlation analysis in p–Pb collisions, two-particle angular correlations between trigger particles in the forward pseudorapidity range and associated particles in the central range are studied. In high-multiplicity events, the double-ridge structure, previously observed in two-particle angular correlations at midrapidity, is also found in the pseudorapidity ranges studied in this analysis. The observations further characterize the collective features in a small collision system. In the analysis of the azimuthal collectivity of longitudinal structures in Pb–Pb collisions, the newly developed method is applied to investigate correlations among the longitudinal structures of produced particles in different azimuthal regions. In addition to the expansion of the QGP in the transverse direction, the initial geometry and resulting longitudinal expansion as a function of azimuthal angle enable us to better understand the full 3-dimensional evolution of heavy-ion collisions.