Browsing by Author "Wilson, Robert J., committee member"
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Item Open Access Design, simulation, and prototyping of wavelength-shifting plate light collector for a large water Cherenkov detector(Colorado State University. Libraries, 2014) Johnston, William Albert, author; Buchanan, Norm, advisor; Wilson, Robert J., committee member; Sites, James, committee member; Menoni, Carmen, committee memberA wavelength-shifting plate light collector has been investigated for a proposed water Cherenkov detector for the Long-Baseline Neutrino Experiment. Experimental prototypes were fabricated from four different wavelength-shifting plastics and tested under uniform illumination as well as with a point source scanner. These laboratory tests were used to study the wavelength and position dependence of the plate's light collection. These results were then used to develop an optical model for the plates that was then used to estimate their effect on measuring neutrino events in the full water Cherenkov detector simulation. These results showed that it was possible to guide between 34% and 49% extra light to a 12" hemispherical PMT. In addition the plates were not found to adversely affect the particle identification abilities of the detector.Item Open Access Imaging individual barium atoms in solid xenon by scanning of a focused laser for use in the nEXO experiment(Colorado State University. Libraries, 2019) Chambers, Christopher, author; Fairbank, William, advisor; Lee, Siu Au, committee member; Wilson, Robert J., committee member; Van Orden, Alan, committee memberNeutrinoless double beta decay (0νββ) is a non-standard model decay process in which two simultaneous beta decays occur, with no emission of neutrinos. This decay is of great interest. If observed, it will demonstrate that the neutrino and anti-neutrino are not distinct. This decay also violates lepton number conservation, a requirement for some theories seeking to explain the matter-antimatter asymmetry of the universe. A measurement of the decay half-life will also give information on the absolute mass scale of the neutrinos. EXO-200 and nEXO use liquid xenon (LXe) time projection chambers (TPC) to search for 0νββ decay. EXO-200 first observed two neutrino double beta decay (2νββ) in xenon-136, the rarest decay ever observed. A low background measurement is vital to maximizing sensitivity to the 0νββ decay mode, yet to be observed. In this dissertation, research and development of a technique for positive identification of the barium-136 daughter (barium tagging) is presented. It is desirable to incorporate barium tagging into the future nEXO detector, as it provides discrimination against all background except for the 2νββ decay mode. The scheme being developed in this work involves extraction of the barium daughter in solid xenon with a cryogenic probe, followed by matrix-isolation fluorescence spectroscopy to tag the barium atom. This work focuses on the detection of individual barium atoms in a prepared solid xenon sample. Single atom sensitivity has been achieved, and a method for imaging of individual atoms by scanning of a focused laser has been demonstrated.Item Open Access Magmatism, deformation, and mineralization along the intra-arc Atacama fault system, northern Chile(Colorado State University. Libraries, 2020) Seymour, Nikki M., author; Singleton, John S., advisor; Kuiper, Yvette D., committee member; Hannah, Judith L., committee member; Ridley, John R., committee member; Wilson, Robert J., committee memberOblique plate motion is nearly universal across subduction margins, and the lateral component of motion produced by oblique subduction may be accommodated through distributed strain and/or along crustal-scale strike-slip faults in the overriding (upper) plate. Magmatic arcs, another fundamental features of the upper plate, have been suggested to play a key role in the initiation and development of localized intra-arc crustal-scale faults. Significant hydrothermal fluid flow derived from arc plutons has also produced world-class metal deposits along intra-arc faults, and may suggest the processes responsible for the initiation, continued deformation, and eventual abandonment of strike-slip faults may also play an important role in focusing economic mineralization. Here I study the sinistral Atacama fault system (AFS), a fossil intra-arc strike-slip fault that occurs within the Mesozoic Coastal Cordillera arc to better understand how oblique plate motion is accommodated in the upper plate and related to arc magmatism. Mapping along the northern ~70 km of the El Salado segment of the AFS documents the distribution of arc plutons and style of deformation. Petrology, geochemistry, and geo/thermochronology were used to characterize and correlate plutons, and structural data were analyzed to understand progressive changes in the style of deformation. New zircon U-Pb dates document a major pulse of magmatism from 150–120 Ma, with the 135–119 Ma plutons most directly tied to AFS ductile deformation. Mylonitic fabrics along the AFS are uniquely associated with the margins of Early Cretaceous plutons, and are cut by late kinematic intrusions at 120–110 Ma. Steeply dipping N- to NE-striking mylonitic fabrics with sinistral shear sense indicators strike ~8–12° clockwise of the steeply dipping, N- to NW-striking AFS strands, indicating deformation occurred during progressive ductile to brittle sinistral strain. The distinctive synkinematic Cerro del Pingo tonalite was mapped on both sides of the eastern branch of the El Salado segment. Petrography, geochemistry, and geochronology all overlap within error, and therefore I interpret two sinistrally separated exposures of the Cerro del Pingo Complex as an offset marker along the AFS. In addition, I correlate a chain of offset leucocratic granites and hypabyssal intrusions across the western branch of the El Salado segment. The sinistral slip magnitude across the entire the El Salado segment is ~50 ± 6 km and occurred almost entirely between ~133 and ~110 Ma at an average slip rate of ~2.0–2.5 km/Myr. I postulate that thermal softening as a result of Early Cretaceous pluton intrusion into the shallow crust locally elevated geothermal gradients, allowing for ductile deformation at ~5–7 km depths. Spatially variable Early Cretaceous pluton emplacement set up a heterogeneous rheology that produced a segmented system that never evolved into a single regional-scale fault. Zircon (U-Th)/He dates record cooling through ~180°C by 116–99 Ma and relaxation of elevated gradients coeval with the end of slip along the El Salado segment. Along the central El Salado segment ~150–200 km south of the offset Cerro del Pingo Complex tonalites, clear fault branches no longer define the AFS. The main branch of AFS in this region is defined by a ~200–500-m-thick steeply NW-dipping shear zone that does not show evidence for brittle overprint. Zircon U-Pb dates document synkinematic emplacement of a tonalite in the shear zone at ~122 Ma. Kinematic indicators record oblique sinistral-reverse shear, but locally coaxial fabrics dominate, indicating an overall transpressional regime. Shear zone activity overlaps in age with other sections of the AFS. The tonalite records a synkinematic sodic-calcic assemblage of actinolite+epidote+titanite+plagioclase, but mylonitic microstructures are completely annealed. The shear zone is cut by an unstrained ~115 Ma diorite body that contains pervasive actinolite+epidote+andradite+plagioclase sodic-calcic mineralization. Similar hydrothermal alteration assemblages are also present ~20 km east of the AFS in the economic Punta del Cobre copper district near Copiapó. The absence of brittle faulting is likely related to continued magmatism associated with the Copiapó batholith complex, which is younger than most arc plutons in the Coastal Cordillera. Postkinematic mineralization along the AFS is unique to the Copiapó area, and magmatic fluids responsible for alteration were most likely derived from the Copiapó batholith. Together, these data document the development of the AFS as a highly segmented fault system that localized mineralization and slipped at a relatively slow rate over ~20 Myr, and was abandoned as plate motion vectors shifted in the middle Cretaceous and arc magmatism migrated eastward.Item Open Access Measurement of the muon anti-neutrino charged current double differential cross section with no pions in the final state on water using the pi-zero detector at T2K(Colorado State University. Libraries, 2018) Campbell, Thomas, author; Toki, Walter, advisor; Biedron, Sandra, committee member; Buchanan, Norm, committee member; Wilson, Robert J., committee memberThe T2K (Tokai to Kamioka) experiment is a long baseline neutrino oscillation experiment where a narrow band (by energy) neutrino beam of primarily muon neutrinos or muon anti-neutrinos is produced in Tokai and directed towards Kamioka in Japan. Neutrinos in the beam are first detected at the T2K near detector complex 280 m from the beam source (ND280) and then travel 295 km before being detected again at the Super-Kamiokande (Super-K) water-Cherenkov detector. In addition to measuring the flux of neutrinos in the T2K beamline en route to Super-K, other physics analyses are performed at ND280. This thesis describes one such measurement where the π0-detector (P∅D) and a time projection chamber at ND280 were used to measure the charged-current cross section for muon anti neutrinos with water as the interaction target and no pions in the final state. Such a cross section is a T2K and world first. This cross section was measured differentially by the outgoing lepton true kinematics using a binned likelihood fitting framework recently developed at T2K. The thesis will provide: an introduction to neutrinos in the context of a cross section measurement, a description of the T2K experiment including common software tools used in analysis, a general discussion of concerns in differential cross section measurements, a mathematical formulation of the likelihood fitting procedure, details of the neutrino event selection process, the chosen parameterization and validation of the fit, and finally, the cross section results in data with a discussion of the significance and conclusions of the measurement. The total cross section integrated over all differential bins considered in the analysis is measured to be: σ = (7.844 ± 1.316) × 10−39 cm2/water molecule.Item Open Access Search for an anomalous excess of charged-current electron neutrino interactions with the MicroBooNE detector(Colorado State University. Libraries, 2022) Caro Terrazas, Ivan, author; Mooney, Michael R., advisor; Wilson, Robert J., committee member; Buchanan, Norm, committee member; Kirby, Michael, committee memberMicroBooNE is a liquid argon time projection chamber detector designed to address the excess of low-energy electromagnetic events observed by the MiniBooNE detector. Electron neutrinos can create a wide variety of topologies when interacting with liquid argon; this analysis measures events without pions, both with (1eNp0π) and without (1e0p0π) visible protons. This thesis presents a first measurement of pionless charged-current electron neutrino interactions from the Booster Neutrino Beam at Fermilab in the MicroBooNE detector. A model based on the MiniBooNE result is used to quantify the strength of the electron neutrino excess. The analysis suggests that if an excess is present, it is not consistent with a simple scaling of the electronneutrino contribution to the flux. Combined, the 1eNp0π and 1e0p0π channels do not give a conclusive indication of the tested model, but separately they both disfavor the low-energy excess model at > 90% CL. The observation in the most sensitive 1eNp0π channel is below the prediction and is consistent with no excess. In the less sensitive 1e0p0π channel the observation at low energy is above the prediction, while overall there is agreement over the full energy spectrum.