Past Event: Dissertation Defense: Youqi Song, Yale University

Probing the parton shower and hadronization through jet substructure measurements at STAR

In high energy collisions, jets can be created from the parton shower and hadronization of energetic quarks and gluons. Studies of the internal structure of jets, known as jet substructure, can provide insight into Quantum Chromodynamics (QCD). This thesis focuses on measurements of jet substructure observables that are sensitive to the theoretically challenging non-perturbative effects of jet evolution. The charge correlator ratio observable, c, which aims to probe hadronization through the charge correlation between the leading and subleading charged particles in jets, is measured in √s = 200 GeV p+p collisions at STAR. The CollinearDrop groomed jet mass, which examines the soft and wide-angle radiation in the parton shower, is also measured, together with six other substructure observables. The measurement is corrected for detector effects using a novel machine-learning driven technique called MultiFold, which preserves the multi-dimensional correlation among the observables.

The deconfined state of QCD matter, known as the quark-gluon plasma (QGP), can be created in high energy nuclear collisions. Measurements of jets created in these collisions may shed light on the properties of the QGP and emergent phenomena of QCD in general. I also present an analysis of r_c with jets in √s_NN = 200 GeV Ru+Ru and Zr+Zr collisions to probe for potential modification of the jet evolution due to interaction with the QGP.

Thesis committee: Helen Caines (advisor), John Harris, Ian Moult, Sarah Demers, and Wenqing Fan (external)