Date of Award
Spring 2023
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Physics
First Advisor
Caines, Helen
Abstract
At extremely high temperature and energy density, the quarks and gluons that make up protons and neutrons become asymptotically deconfined and form a novel state of matter called the Quark-Gluon Plasma (QGP). This state of matter is experimentally created in relativistic heavy-ion collisions, where the high energy density carried by the incoming nuclei produce such a deconfined state.The QGP has been widely confirmed and studied in large collision systems like Au+Au and Pb+Pb, but whether the QGP exists in small systems like $p$+Au, and the dependence of QGP production on the collision system size are still open questions in the field. One way to study the QGP properties is by using proxies of high energy partons created in the initial stages of the collisions. Partons are colored quarks and gluons, and they fragment into color-neutral hadrons in the final state. These high momentum partons lose energy while traveling through the QGP, and the impact of these interactions can be reflected via the modified hadron yields. By contrasting hadron spectra in $p$+$p$ to those in A+A we can determine the amount of modification from the medium which informs us about the QGP properties. In this thesis, I report studies on charged hadron yields in Ru+Ru, Zr+Zr and $p$+Au collisions at $\sqrt{s_{NN}}$=200 GeV with the STAR detector at RHIC, as functions of momentum and number of participating nucleons $N_part$. The yields are measured differentially in centrality/event activity, and their comparison with the $p$+$p$ hadron yield, the nuclear modification factors, are reported. Enhancement in $p$+Au collision yields is reported, which is expected from initial state effects. In Ru+Ru/Zr+Zr, significant suppression is seen in central collisions. The suppression weakens gradually moving to more peripheral collisions, until a geometric bias from the centrality estimation complicates the interpretation. Using this bias, we can explore the limitations of the Glauber model on the peripheral end, which in this thesis we provide a direction to improve on going forward. The results are compared with measurements in other collisions systems at STAR, and a continuous picture of parton energy loss in the QGP environment as a function of system size is extracted, which is found to be highly correlated with $N_part$. Comparison with theoretical models are also made, and potential future measurements are discussed.
Recommended Citation
Liu, Tong, "Inclusive Hadron Yield Analysis in Small and Mid-sized Collision Systems at Center-of-Mass Collision Energy of 200 GeV per Nucleon at STAR" (2023). Yale Graduate School of Arts and Sciences Dissertations. 1327.
https://elischolar.library.yale.edu/gsas_dissertations/1327
