Jet radius and rapidity dependence of azimuthal correlations in photoproduced dijets

Ultraperipheral heavy ion collisions at the Large Hadron Collider provide a source of polarized photons that can be used to probe Pb nuclei. The primary work presented in this dissertation makes use of such collisions to study the angular distribution of photoproduced dijets as a function of the azimuthal angle φ between the sum, Qₜ, and difference, Pₜ, of the jet transverse momenta. The second and fourth moments of the distribution, ⟨cos(2φ)⟩ and ⟨cos(4φ)⟩, were measured as a function of dijet transverse momentum and rapidity for different jet radii. The data used were recorded by the CMS detector during the 2018 PbPb run, having a center-of-mass energy per nucleon of 5.02 TeV and an integrated luminosity of 1.67 nb⁻¹. Events were classified by their pattern of neutron production in the Zero Degree Calorimeters as either having no neutrons on both sides (0n0n) or at least one neutron opposite the direction of the photon (0nXn). For jets of radius 0.4, ⟨cos(2φ)⟩ was found to be positive and independent of the neutron topology, suggesting a common underlying mechanism for generating angular asymmetries in both photonuclear and photodiffractive enhanced events. The data were compared to predictions from the PYTHIA Monte Carlo, version 8.311 for photonuclear interactions. In both data and PYTHIA, increasing ⟨cos(2φ)⟩ and ⟨cos(4φ)⟩ values were observed with decreasing jet radius, demonstrating a greater sensitivity in smaller jets to final state radiation effects. PYTHIA was found to model the data well, with the exception of underestimated ⟨cos(2φ)⟩ values for r = 0.2 jets. For both bins of Qₜ, ⟨cos(2φ)⟩ and ⟨cos(4φ)⟩ values in PYTHIA showed signs of rapidity dependence. In data, ⟨cos(2φ)⟩ was found to be independent of rapidity for Qₜ < 12 GeV, but dependent on rapidity for Qₜ > 12 GeV. Due to large statistical error bars, ⟨cos(4φ)⟩ values were found to be independent of rapidity in both Qₜ bins. Finally, this dissertation also contains summaries on service work performed for CMS relating to methods for determining luminosity and the Zero Degree Calorimeters.

Name thesis:degree_name

Ph.D.

Discipline thesis:degree_discipline

Physics & Astronomy

Grantor dc:publisher

University of Kansas

Year dc:date.issued

2025

Author dc:creator

• Le Mahieu, Cole

Advisor dc:contributor.advisor

• Murray, Michael

• CMS
• Heavy Ions
• Jets

Statement dc:rights

• This item is protected by copyright and unless otherwise specified the copyright of this thesis/dissertation is held by the author.

Language dc:language.iso

en

Dc Identifier Other

https://www.proquest.com/LegacyDocView/DISSNUM/32443070

OAI identifier oai:identifier

oai:kuscholarworks.ku.edu:1808/36335