Browsing by Author "Toki, Walter, committee member"
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Item Open Access A spectral analysis of the Crab nebula and other sources with HAWC(Colorado State University. Libraries, 2016) Gussert, Michael, author; Harton, John, advisor; Mostafa, Miguel, advisor; Toki, Walter, committee member; Anderson, Chuck, committee member; Gelfand, Martin P., committee memberThe High Altitude Water Cherenkov observatory (HAWC) is an extensive air shower particle detection array designed to study cosmic gamma (γ) rays in the Very High Energy (VHE) regime (100 GeV to 100 TeV). One of the most thoroughly studied sources in this energy range is the Crab nebula, a pulsar wind nebula created by the aftermath of supernova 1054. The core of this analysis revolves around the determination of the differential flux spectrum of the Crab nebula using a process known as forward folding. Forward folding allows energy spectra to be fit without requiring a direct measurement of the primary energy of individual extensive air showers. The energy resolution of HAWC is very poor (on the order of 50% or more), and so this method is ideal for any spectral analysis carried out with HAWC data. The differential spectra are modeled as a power law with a normalization (Φ0), spectral index (γ), and a cutoff energy (Ec): dN/dE = Φ0(E/E0)γe−E/Ec . The normalization of the Crab nebula was found to be 1.03±0.091 0.083 stat ±0.19 sys)×10−12(TeV−1 cm−2 s −1 ) with an index of −2.54 ± 0.095 stat ± 0.27 sys and a cutoff of 91.0 ±174 59 stat with E0 =4.0 TeV. This method was also applied to 11 other sources, and the minimum detection significance required to constrain a spectrum was found to be between 10 and 14 σ.Item Open Access Calibration of the Pierre Auger Observatory fluorescence detectors and the effect on measurements(Colorado State University. Libraries, 2015) Gookin, Ben, author; Harton, John, advisor; Toki, Walter, committee member; Buchanan, Kristen, committee member; Menoni, Carmen, committee memberThe Pierre Auger Observatory is a high-energy cosmic ray observatory located in Malargue, Mendoza, Argentina. It is used to probe the highest energy particles in the Universe, with energies greater than 10¹⁸ eV, which strike the Earth constantly. The observatory uses two techniques to observe the air shower initiated by a cosmic ray: a surface detector composed of an array of more than 1600 water Cherenkov tanks covering 3000 km², and 27 nitrogen fluorescence telescopes overlooking this array. The Cherenkov detectors run all the time and therefore have high statistics on the air showers. The fluorescence detectors run only on clear moonless nights, but observe the longitudinal development of the air shower and make a calorimetric measure of its energy. The energy measurement from the the fluorescence detectors is used to cross calibrate the surface detectors, and makes the measurements made by the Auger Observatory surface detector highly model-independent. The calibration of the fluorescence detectors is then of the utmost importance to the measurements of the Observatory. Described here are the methods of the absolute and multi-wavelength calibration of the fluorescence detectors, and improvements in each leading to a reduction in calibration uncertainties to 4% and 3.5%, respectively. Also presented here are the effects of introducing a new, and more detailed, multi-wavelength calibration on the fluorescence detector energy estimation and the depth of the air shower maximum measurement, leading to a change of 1±0.03% in the absolute energy scale at 10¹⁸ eV, and a negligible change in the measurement on shower maximum.Item Open Access Cosmogenic background rejection for the sterile neutrino search with the Short-Baseline Neutrino Program far detector(Colorado State University. Libraries, 2020) Hilgenberg, Christopher M., author; Wilson, Robert J., advisor; Harton, John, committee member; Toki, Walter, committee member; Zhu, Wen, committee memberAs the Short-Baseline Neutrino Program Far Detector, the ICARUS liquid argon time-projection chamber will operate at shallow depth and therefore be exposed to the full surface flux of cosmic rays. This poses a problematic background to the sterile neutrino search. A direct way to reject this background is to surround the cryostat with a detector capable of tagging incident cosmic muons with high efficiency, the Cosmic Ray Tagging System (CRT). I have worked to develop the CRT detector hardware and the simulation and reconstruction software. This system, currently undergoing installation, is approximately 25% commissioned and taking data. I have developed a powerful method for cosmogenic background rejection utilizing the CRT and Photon Detection System. Results from a simulation based study, informed by CRT data, demonstrate the power of the technique in rejecting cosmogenic events with little adverse impact on the neutrino sample.Item Open Access In-situ laser tagging of barium ions in liquid xenon for the EXO experiment(Colorado State University. Libraries, 2012) Hall, Kendy, author; Fairbank, William, advisor; Toki, Walter, committee member; Marconi, Mario, committee member; Roberts, Jacob, committee memberThe goal of the Enriched Xenon Observatory (EXO) collaboration is to measure the half-life of neutrino-less double beta decay using a ton size liquid 136Xe detector with zero back-ground. Zero background detection can only be achieved if the daughter nucleus, 136Ba, can be tagged. The EXO collaboration is investigating several techniques to tag the 136Ba daughter. The goal of this thesis is to investigate the prospects of directly observing a single 136Ba+ ion in the liquid using a laser aimed at the decay site, hence in-situ laser tagging. Because the energy levels of Ba+ ions are expected to be altered from the vacuum configuration, in-situ laser tagging can only be accomplished if the spectroscopy of the Ba+ ions in liquid xenon is understood. An ultra-pure liquid xenon test apparatus with a liquid xenon purity monitor has been built to study the spectroscopy of the Ba+ ions. An unexpected discovery of the nonresonant multiphoton ionization of liquid xenon using pulsed UV lasers was made while characterizing the purity monitor. The discovery was vital to the ability to accurately measure the purity of the liquid xenon. The spectroscopy of Ba+ ions in liquid xenon and the multiphoton ionization studies are the two key topics that are presented in this thesis.Item Open Access Measurement of the differential charged current single pion cross section using muon momentum and muon angle in the pi zero detector of the T2K experiment(Colorado State University. Libraries, 2018) Schwehr, Jaclyn, author; Wilson, Robert J., advisor; Berger, Bruce, committee member; Toki, Walter, committee member; Mooney, Michael, committee member; Brandl, Alexander, committee memberA measurement of the charged current single pion differential cross section in the pi-zero detector of the T2K experiment is presented as a function of reconstructed muon momentum and muon angle. This measurement is done with particular care taken to minimize model dependence throughout the analysis, specifically with careful signal definition and efficiency corrections. New methods for improving the reconstruction of low energy pions are included, as is a method for fitting background events induced by signal physics without introducing model dependence to the fit. Run 4 water-in data is used to make this measurement, which corresponds to an exposure of 1.63×1020 protons on target. The differential cross section measurement is made per nucleon for all targets in the fiducial volume of the pi-zero detector over muon angles of 0◦ to 90◦ with respect to the incident neutrino beam direction, and muon momenta from 150 MeV to 5 GeV. The measured cross sections are lower than those predicted by the default Rein Sehgal resonance and coherent models, favoring the Minoo resonance and Berger Sehgal coherent models.Item Open Access Measurement of νμ-induced charged-current single π⁺ production on H₂O(Colorado State University. Libraries, 2015) Assylbekov, Shamil M., author; Wilson, Robert J., advisor; Toki, Walter, committee member; Harton, John, committee member; Berger, Bruce, committee member; Hulpke, Alexander, committee memberT2K is an international collaboration that has constructed an experiment in Japan to investigate the properties of the neutrino. It consists of two near detectors, ND280 and INGRID, and a far detector - Super-Kamiokande. ND280 has multiple sub-detectors with the π⁰ detector (PØD) being of most importance to this analysis. This work describes the first measurement of neutrino cross section for charged-current single positively charged pion (CC1π⁺) interaction channel on water (H₂O) using the PØD as target and detector. The PØD detector has been taking neutrino interaction data since 2009 in configurations with and without an integrated water target. Using a statistical water-in/water-out event rate subtraction, a measurement of the νμ-induced CC1π⁺ cross section on water is reported to be ‹σ› = 1.10 x 10⁻³⁹ +0.39·10⁻³⁹/-0.36·10⁻³⁹ cm², where the result is provided in the form of a single-bin cross section integrated over the entire T2K neutrino energy range. The measurement is based on a sample of 2,703 events selected from beam runs of $2.64 x 10²⁰ protons-on-target (POT) with the PØD water-in configuration, and 2,187 events selected from $3.71 x 10²⁰ POT with the water-out configuration. The corresponding Monte Carlo simulation predicted numbers of background events to be 1,387.2 and 1,046.0 for the water-in and water-out detector configurations, respectively. The accuracy of the result is dominated by flux and cross section models uncertainties. The data favors a systematically smaller cross section when compared to the model but within the uncertainties it is consistent with the Monte Carlo simulation prediction of $1.26 x 10⁻³⁹cm². The result, its significance, and the strategy for future CC1π⁺ measurements are discussed in conclusion.Item Open Access Neutrino oscillation parameter sensitivity in future long-baseline experiments(Colorado State University. Libraries, 2014) Bass, Matthew, author; Wilson, Robert J., advisor; Harton, John, committee member; Toki, Walter, committee member; Zhou, Wen, committee memberThe study of neutrino interactions and propagation has produced evidence for physics beyond the standard model and promises to continue to shed light on rare phenomena. Since the discovery of neutrino oscillations in the late 1990s there have been rapid advances in establishing the three flavor paradigm of neutrino oscillations. The 2012 discovery of a large value for the last unmeasured missing angle has opened the way for future experiments to search for charge-parity symmetry violation in the lepton sector. This thesis presents an analysis of the future sensitivity to neutrino oscillations in the three flavor paradigm for the T2K, NOνA, LBNE, and T2HK experiments. The theory of the three flavor paradigm is explained and the methods to use these theoretical predictions to design long baseline neutrino experiments are described. The sensitivity to the oscillation parameters for each experiment is presented with a particular focus on the search for CP violation and the measurement of the neutrino mass hierarchy. The variations of these sensitivities with statistical considerations and experimental design optimizations taken into account are explored. The effects of systematic uncertainties in the neutrino flux, interaction, and detection predictions are also considered by incorporating more advanced simulations inputs from the LBNE experiment.Item Open Access Quantification of the directional detection capability of the DRIFT-IIe dark matter search detector via the range of nuclear recoil tracks in two dimensions(Colorado State University. Libraries, 2021) Schuckman, Frederick G., II, author; Harton, John, advisor; Toki, Walter, committee member; Mooney, Michael, committee member; Marconi, Mario, committee memberEvidence suggests that 83% of the matter content of the universe is dark matter. Despite its ubiquity, the identity of this matter is unknown. It is thought that a halo of dark matter surrounds and is distributed throughout our galaxy. The Weakly Interacting Massive Particle (WIMP) has been a popular dark matter candidate. As we move through this halo it should appear as a wind of WIMPs incident upon us. A properly-placed detector could have this wind blow through its top face at one time in the day, and through a side face 12 sidereal hours later. DRIFT-IIe is a low-pressure gas negative-ion time projection chamber designed for direct and directional detection of WIMPs elastically scattering from gas nuclei. Partial directional information of a WIMP recoil could be extracted by measuring the range of the track of ionization that it produces in two dimensions. To study this signature, the detector was exposed to a source of neutrons in a series of runs. In one run the source was placed above the detector and in a second run the source was placed to the side of the detector. Neutron recoils mimic those expected from WIMPs, and the source placement mimics a specific WIMP wind direction. For the two runs, the range information was compared with a Monte Carlo resampling test. It was found on average 302 +/- 4 neutron recoils, sampled with WIMP-like energy spectra, are required along each of these axes to discern the two populations with a significance of 3σ.Item Open Access The Möbius number of the symmetric group(Colorado State University. Libraries, 2012) Monks, Kenneth M., author; Hulpke, Alexander, advisor; Penttila, Tim, committee member; Achter, Jeff, committee member; Toki, Walter, committee memberThe Möbius number of a finite group is its most important nontrivial combinatorial invariant. In this paper, we compute the Möbius numbers of many partially-ordered sets, including the odd-partition posets and the subgroup lattices of many infinite families of groups. This is done with an eye towards computing the Möbius number of the symmetric group on 18 points.