Doctoral Dissertations

Date of Award

5-2024

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Physics

Major Professor

Christine Nattrass

Committee Members

Nadia Fomin, Maik Lang, Larry Lee

Abstract

At the CERN Large Hadron Collider, protons and heavy ions are collided at relativistic
speeds in order to study the behavior and processes of Quantum Chromodynamics (QCD). One such process is the production of collimated sprays of particles called jets resulting from the hard scattering of two partons. Jets are an important probe that provide a window into the early stages of the collision.

Measurements in small systems such as proton-proton (pp) and proton-lead (p–Pb)
collisions are important in order to provide constraints on nuclear parton distribution
functions and the strong coupling constant αS [55]. Measurements at different center of mass energies can improve constraints and find deviations from their predictions. In addition, jet production in proton-proton collisions can be used as a reference for more complex systems, such as the environments produced in p–Pb and Pb–Pb collisions. Both of these systems are subject to cold nuclear matter effects, while in Pb–Pb collisions, the presence of a strongly-interacting medium plays a major role. While such a medium is not expected in small collision systems such as p–Pb, recent studies suggest the presence of collectivity.

In this analysis, pp collisions at a center of mass energy of 8 TeV and p–Pb collisions at a center of mass energy of 8.16 TeV are investigated in order to study the systems individually and shed light on potential differences. The differential jet cross-sections are presented for fully reconstructed jets with resolution parameter R = 0.2 to 0.5 in pp collisions at √s = 8 TeV and R = 0.2 to 0.4 in p–Pb collisions at √sNN = 8.16 TeV. Cross-section ratios are shown between R = 0.2 jets and the other resolution parameters. The nuclear modification factor, RpPb, is calculated to study the impact of including a nucleus in the collision. The RpPb is defined as the ratio of the jet yield in p–Pb to pp collisions, scaled by the number of binary nucleon-nucleon collisions. Comparisons are made to PYTHIA8 Monash and POWHEG+PYTHIA8.

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