Aric Tate, Ph.D. Candidate
Dr. Matthias Grosse Perdekamp, Co-Director of Research
Dr. Riccardo Longo, Co-Director of Research
December 8, 2023 | 9:30am - 11:30am CST
This final examination will be held in 101A Talbot Laboratory.
INVESTIGATIONS OF INITIAL STATE EFFECTS IN p+Pb COLLISIONS VIA DIJET
MEASUREMENTS WITH THE ATLAS DETECTOR
ABSTRACT:
The Large Hadron Collider (LHC) at the European Organization for Nuclear Research is the most powerful particle accelerator in the world. The ATLAS experiment, located on the LHC, is a multi-purpose detector with ∼ 4π coverage, providing tracking and calorimetry for particles generated by relativistic collisions of protons and/or nuclei. The ATLAS Collaboration uses the recorded data to test the limits of our understanding of physics, searching for new particles and investigating the fundamental structure of matter. The study of heavy ion collisions at the LHC has informed our understanding of the quark-gluon plasma (QGP), a deconfined state of matter formed at high temperature and density, in which partons collectively behave as a liquid. To disentangle initial-state effects from final-state effects originating from the QGP, proton-lead (p+Pb) collisions are studied. In such collisions, QGP formation does not occur, allowing for examination of initial-state nuclear effects. By making use of the full acceptance of the ATLAS calorimeter, dijet probes in p+Pb collisions can be used to characterize initial-state effects in terms of the hard-scattering kinematics.
This thesis represents the first measurement of the centrality dependence of the triple-differential dijet yield using 165 nb−1 of p+Pb data collected at √sNN = 8.16 TeV in 2016. In collider experiments, jets are collimated sprays of particles originating from high momentum transfer collisions. In a given event, the two jets with the largest transverse momentum are referred to as a dijet. The event centrality, which is directly related to the number of inelastic collisions between the incident proton and the nucleons bound in the Pb nucleus, is characterized by the total transverse energy measured in the Pb-going calorimeter near to the beam axis. The dijet yield is measured as a function of the average transverse momentum of the jet pair, the boost of the dijet system, and the half rapidity separation between the jets. The central-to-peripheral ratio of the dijet yields, RCP, is evaluated, and the results are presented as a function of variables that reflect the kinematics of the initial hard parton-parton scattering process. The RCP shows a scaling with the Bjorken-x of the parton originating from the proton, xp, while no such trend is observed as a function of xPb. These results represent a unique input to further understand xp-dependent color fluctuation effects, where small proton configurations are characterized by a reduced interaction strength that results in less soft proton-nucleus collisions and, therefore, a biased centrality. Results are then used to further interpret previous, less differential, p+Pb measurements that were performed at a lower center-of-mass energy.
