## Physics and Astronomy Dissertations

#### Author ORCID Identifier

https://orcid.org/ 0000-0002-1021-2555

Spring 5-2-2022

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

#### Department

Physics and Astronomy

Megan Connors

#### Abstract

Ultrarelativistic heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) allow for a novel environment in which to study the fundamental interaction between quarks and gluons, known as the nuclear strong force. The strong force ordinarily confines quarks and gluons (“partons”) to the interior of composite particles such as protons and neutrons (hadrons”), but, in heavy-ion collisions, energy densities become sufficiently high that hadrons effectively melt into a plasma of free partons known as a Quark Gluon Plasma (QGP). Quantifying the properties of the QGP, such as its bulk viscosity, temperature, and entropy-to-shear-viscosity ratio have become key endeavors of high energy nuclear physics in the past two decades. Additionally, quantification of the strength of the color field (the strong interaction analogy of the electromagnetic field) and how energy permeates through the plasma itself is necessary. This dissertation focuses on the latter set of objectives through the use of an experimental observable known as “jets”, which are collimated sprays of particles. Additionally, jets in heavy-ion collisions have been found to have both their momentum and their shape modified relative to jets found in proton-proton collisions, where there is no QGP formation. This jet modification occurs because the parent partons of the jets have themselves been modified by the interaction with the color field inside the QGP. Thus, studying jet modification allows us to quantify properties of the QGP itself. This dissertation presents the results of examining angular correlations between jet fragments and high momentum neutral pions ($\pi^0$). Correlating jet fragments to a high momentum $\pi^0$ allows for high statistical precision, as neutral pions are one of the most abundant particles created in heavy-ion collisions. A high momentum ($p_T \geq 12$~GeV/c) $\pi^0$ can also carry up to 80$\%$ of a single jet’s momentum, making them very good proxies for the jet itself kinematically. This work will utilize the largest heavy-ion data set available from the PHENIX detector, collected during 2014, containing approximately 20 billion Au+Au events.

#### DOI

https://doi.org/10.57709/28846024