Thesis (M.S.)--University of Michigan, 1966.

Thesis (Ph. D.)--Florida State University, 2002. / Advisor: Dr. Horst Wahl, Florida State University, College of Arts and Sciences, Dept. of Physics. Title and description from dissertation home page (Oct. 6, 2003). Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 1997. / Vita. Includes bibliographical references (p. [107]-111).

A search for the production of three massive vector bosons with at least one Z boson is presented. 140 fb⁻¹ of pp collisions at center-of-mass energy sqrt(s) = 13 TeV collected with the ATLAS detector at the LHC from 2015 to 2018 are analyzed. Events with three leptons and at least one reconstructed jet are discussed, targeting the WWZ → lνqqll and WZZ → lνqqll decay channels. Evidence for the searched-for production process is observed. Additional results demonstrating the combination of the three lepton search with searches including four or more leptons are shown. Pending the unblinding and combination of these results, there is potential for the discovery of the searched-for production process.

Measurements of the jet substructure in Pb+Pb collisions provide information about the mechanism of jet quenching in the hot and dense QCD medium created in these collisions, over a wide range of energy scales. Recent measurements of the nuclear modification factor of large-radius jets in 5.02 TeV Pb+Pb collisions with ATLAS are presented. 2017 pp data of 257 inverse picobarns and 2018 Pb+Pb data of 1.72 inverse nanobarns are used in these measurements. The R=1.0 large-radius jets are reconstructed with the anti-kt algorithm from R=0.2 anti-kt jets. In each large-radius jet, the associated R=0.2 jets, as constituents, are re-clustered using the kt algorithm to obtain the earliest splitting substructure observables, including the splitting scale sqrt(d12) and the angular separation dR. The nuclear modification factor RAA, which is the jet yield suppression in Pb+Pb compared to pp, is measured as a function of the jet transverse momentum pt and jet substructure observables sqrt(d12) and dR. A significant RAA decrease for jets with one single sub-jet is observed, compared to jets with more complex substructure. These results support the hypothesis that jets with hard internal splittings losemore energy propagating through the medium. Measurements of RAA with dependence on the jet substructure characterized using charged particle fragments are also presented. Utilizing jets of a consistent definition, the substructure observables, specifically the splitting scale sqrt(d12) and the angular separation dR, are extracted from the kt re-clusterings of charged particles associated to each large-radius jet. The soft-drop grooming algorithm is applied with the kt re-clusterings of the charged particles to mitigate the strong underlying event effects. RAA is found to have a significant decrease with increasing sqrt(d12) and dR at their lower values, suggesting possible color coherence effects influencing the jet energy loss in the medium.

The intense electromagnetic fields surrounding highly charged, ultra-relativistic ions at the LHC provide an intense flux of quasi-real photons. This high-energy photon flux provides a precise probe of the structure of the nucleus in photonuclear interactions and a tool to precisely study the properties of photoproduction in two-photon interactions. This thesis presents recent results from studies of photoproduction processes in √𝒔_𝐍𝐍 = 5.02 TeV Pb+Pb collisions at the LHC, using data collected in 2015 and 2018. A measurement of the differential cross-section for photonuclear jet production is performed with an integrated luminosity of 1.72 nb⁻¹. This measurement is triple-differential in two different sets of kinematic variables ([𝐻_𝐓, 𝒙_𝐀, 𝒛_𝛾] and [𝐻_𝐓, 𝒚_jets, 𝒎_jets) which allow for a direct measurement of the kinematics of struck partons in the nuclear target, and it is fully unfolded in three dimensions. After performing detailed studies of the rate for nuclear breakup in these collisions, the photonuclear jet cross-sections agree with leading-order predictions at the level of 10%. The uncertainty on this measurement and full treatment of its correlated uncertainties will allow for it to significantly constrain the nuclear parton distributions over a wide region of parton kinematics. A measurement was also performed of dimuon production via two-photon fusion in Pb+Pb collisions with nuclear overlap. This measurement studied the relative deflection of muons in each pair, and its results indicated that these distributions are substantially modified as a function of collision centrality. This modification is mostly well-described by initial-state models, which improve the modelling of the photon flux by incorporating correlations between the collision impact parameter and photon 𝒑_𝐓. Additional studies were performed to constrain the potential impact of any deflections due to the presence of strong magnetic fields in the hot, dense medium produced in heavy ion collisions.

A search is presented for hadronic signatures of a strongly-coupled hidden dark sector, accessed via resonant production of a ?′ mediator. The analysis uses 139 fb-1 of proton-proton collision data collected by the ATLAS experiment during Run 2 of the LHC. The ?′ mediator decays to two dark quarks, which each hadronize and decay to showers containing both dark and Standard Model particles; these showers are termed “semi-visible” jets. The final state consists of missing energy aligned with one of the jets, a topology that is ignored by most dark matter searches. A supervised machine learning method is used to select these dark showers and reject the dominant background of mis-measured multijet events. A complementary semi-supervised anomaly detection approach introduces broad sensitivity to a variety of strongly coupled dark matter models. A resonance search is performed by fitting the transverse mass spectrum with a polynomial background estimation function. Results are presented as limits on the effective cross section of the Z', parameterized by the fraction of invisible particles in the decay and the Z' mass. No structure in the transverse mass spectrum compatible with the signal hypothesis is observed. Z' mediator masses from ranging from 2.0 TeV to 3.5 TeV are excluded at the 95% confidence level.

This PhD thesis presents the measurement of the differential cross section for the production of a Z boson in association with jets in proton-proton collisions taking place at the Large Hadron Collider (LHC) at CERN, at a centre-of-mass energy of 8 TeV. A development of a data acquisition (DAQ) system for the Triple-Gas Electron Multiplier (GEM) detector in view of the Compact Muon Solenoid (CMS) detector upgrade is also presented.<p><p>The events used for the data analysis were collected by the CMS detector during the year 2012 and constitute a sample of 19:6 fb-& / Doctorat en Sciences / info:eu-repo/semantics/nonPublished