SNO+

Abstract:

A liquid scintillator consisting of linear alkylbenzene as the solvent and 2,5-diphenyloxazole as the fluor was developed for the SNO+ experiment. This mixture was chosen as it is compatible with acrylic and has a competitive light yield to pre-existing liquid scintillators while conferring other advantages including longer attenuation lengths, superior safety characteristics, chemical simplicity, ease of handling, and logistical availability. Its properties have been extensively characterized and are presented here. This liquid scintillator is now used in several neutrino physics experiments in addition to SNO+.

Abstract:

A liquid scintillator consisting of linear alkylbenzene as the solvent and 2,5-diphenyloxazole as the fluor was developed for the SNO+ experiment. This mixture was chosen as it is compatible with acrylic and has a competitive light yield to pre-existing liquid scintillators while conferring other advantages including longer attenuation lengths, superior safety characteristics, chemical simplicity, ease of handling, and logistical availability. Its properties have been extensively characterized and are presented here. This liquid scintillator is now used in several neutrino physics experiments in addition to SNO+.

Abstract:

Designing high-intensity accelerators has traditionally relied on using computer simulations to study the beam dynamics. As intense beams are comprised of large numbers of particles, all interacting via Coulomb forces, such simulations require significant computational power in order to numerically predict these interactions. The Intense Beams Experiment (IBEX) is a linear Paul trap that can replicate the transverse beam dynamics in accelerators by trapping low-energy ions using RF electric fields that emulate the magnetic focusing elements of particle accelerators. IBEX’s flexibility allows different lattice designs and beam intensities to be tested with ease, which means that it can be used to test novel lattice configurations for high-intensity accelerators. Examples of such lattices arise from the theory of Nonlinear Integrable Optics, and, as discussed in this thesis, the related theory of Quasi-Integrable Optics (QIO). These theories suggest techniques for introducing nonlinear elements such as octupoles into an accelerator lattice, while keeping the system integrable and hence maintaining stable particle motion.

In this work, an upgrade to the original IBEX trap was designed, manufactured, and commissioned with the aim of experimentally testing the principles of QIO. Simulations were used to test the ability of a quasi-integrable lattice to damp a space-charge-driven coherent resonance without exciting the 4th order incoherent resonance in the vicinity. This lattice was then compared to a lattice which broke the integrability conditions, which was shown to excite the 4th order resonance. Using the newly-commissioned IBEX-2 trap, we were then able to test the quasi-integrable lattice experimentally and verify the results from simulations. This thesis demonstrates the first ions successfully trapped in a quasi-integrable lattice in a Paul trap, and discusses the benefits of introducing octupole elements according to the method prescribed by the theory of QIO. The experimental results presented here show the potential value of QIO to research on high-intensity beams in accelerators.

Abstract:

Recent studies have highlighted the potential of jet substructure techniques to identify the hadronic decays of boosted heavy particles. These studies all rely upon the assumption that the internal substructure of jets generated by QCD radiation is well understood. In this article, this assumption is tested on an inclusive sample of jets recorded with the ATLAS detector in 2010, which corresponds to 35 pb^-1 of pp collisions delivered by the LHC at sqrt(s) = 7 TeV. In a subsample of events with single pp collisions, measurementes corrected for detector efficiency and resolution are presented with full systematic uncertainties. Jet invariant mass, kt splitting scales and n-subjettiness variables are presented for anti-kt R = 1.0 jets and Cambridge-Aachen R = 1.2 jets. Jet invariant-mass spectra for Cambridge-Aachen R = 1.2 jets after a splitting and filtering procedure are also presented. Leading-order parton-shower Monte Carlo predictions for these variables are found to be broadly in agreement with data. The dependence of mean jet mass on additional pp interactions is also explored.

Abstract:

The SNO+ experiment collected data as a low-threshold water Cherenkov detector from September 2017 to July 2019. Measurements of the 2.2-MeV $\gamma$ produced by neutron capture on hydrogen have been made using an Am-Be calibration source, for which a large fraction of emitted neutrons are produced simultaneously with a 4.4-MeV $\gamma$. Analysis of the delayed coincidence between the 4.4-MeV $\gamma$ and the 2.2-MeV capture $\gamma$ revealed a neutron detection efficiency that is centered around 50% and varies at the level of 1% across the inner region of the detector, which to our knowledge is the highest efficiency achieved among pure water Cherenkov detectors. In addition, the neutron capture time constant was measured and converted to a thermal neutron-proton capture cross section of $336.3^{+1.2}_{-1.5}$ mb.