Tong Liu successfully defends thesis, “Inclusive Hadron Yield Analysis in Small and Mid-sized Collision Systems at sqrt(s_NN)=200 GeV at STAR”

November 17, 2023

On November 14, Tong Liu successfully defended the thesis “Inclusive Hadron Yield Analysis in Small and Mid-sized Collision Systems at sqrt(s_NN)=200 GeV at STAR” (advisor: Helen Caines).

Liu explained, “The Quark-Gluon Plasma (QGP) is a novel state of matter that is close to what we think the universe looked like within 0.000001 second after the big bang. It can also be produced in heavy-ion collisions, where atomic nuclei are accelerated to nearly the speed of light before colliding with each other. My research focuses on how the production of QGP depends on the size of the collision systems, using the high energy particles produced in these collisions. Specifically, I performed measurements in two medium-sized collision systems and an asymmetric system, and, combining with previous measurements, I found a clear dependence of QGP production on the system size.”

Liu will join SquarePoint Capital as a quantitative researcher.

Thesis Abstract

At extremely high temperature and energy density, the quarks and gluons form a novel state of matter called the Quark-Gluon Plasma (QGP). The QGP has been widely studied via relativistic heavy ion collisions in large collision systems like Au+Au and Pb+Pb. However, 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. One way to study the QGP properties is by using proxies of high energy partons, which are created in the initial stages of the collisions, and fragment into hadrons in the final state. These partons lose energy while traveling through the QGP, which 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 medium modification, 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 200 GeV with the STAR detector at RHIC, and their comparisons with the hadron yield in p+p collisions. The results are compared with previous measurements at STAR as well as theoretical models, and potential future measurements are discussed.

This story was adapted from the Wright Lab news story of November 14, 2023 by Victoria Misenti.