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Browsing by Author "Toki, Walter, advisor"

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    A search for Lorentz and CPT violation in the neutrino sector of the standard model extension using the near detectors of the Tokai to Kamioka neutrino oscillation experiment
    (Colorado State University. Libraries, 2016) Clifton, Gary Alexander, author; Toki, Walter, advisor; Berger, Bruce, committee member; Eykholt, Richard, committee member; Hulpke, Alexander, committee member
    The Tokai to Kamioka (T2K) neutrino experiment is designed to search for electron neutrino appearance oscillations and muon neutrino disappearance oscillations. While the main physics goals of T2K fall into conventional physics, T2K may be used to search for more exotic physics. One exotic physics analysis that can be performed is a search for Lorentz and CPT symmetry violation (LV and CPTV) through short baseline neutrino oscillations. The theoretical framework which describes these phenomena is the Standard Model Extension (SME). Due to its off-axis nature, T2K has two near detectors. A search for LV and CPTV is performed in each detector. The search utilizes charged-current inclusive (CC inclusive) neutrino events to search for sidereal variations in the neutrino event rate at each detector. Two methods are developed; the first being a Fast Fourier Transform method to perform a hypothesis test of the data with a set of 10,000 toy Monte-Carlo simulations that do not have any LV signal in them. The second is a binned likelihood fit. Using three data sets, both analysis methods are consistent with no sidereal variations. One set of data is used to calculate upper limits on combinations of the SME coefficients while the other two are used to constrain the SME coefficients directly. Despite not seeing any indication of LV in the T2K near detectors, the upper limits provided are useful for the theoretical field to continue improving theories which include LV and CPTV.
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    Independent measurement of the T2K near detector constraint using the off-axis pi-zero detector
    (Colorado State University. Libraries, 2019) Hogan, Matthew Gregory, author; Toki, Walter, advisor; Wilson, Robert, committee member; Buchanan, Norman, committee member; Zhou, Wen, committee member
    The Tokai to Kamioka (T2K) experiment is a long-baseline neutrino oscillation experiment hosted in Japan searching for electron neutrino appearance in a high purity muon neutrino beam. In order to constrain the systematic uncertainties in the oscillation analysis, a dedicated near detector (ND) complex called ND280 is located 280 meters from the neutrino production source in line of the beam. To date, the Fine Grain Detector (FGD) in ND280 has provided the ND constraint using a binned maximum likelihood estimate fit. This thesis describes the effort to validate the ND constraint using the same framework, but with an independent data set from the ND280 pi-zero detector (PØD). Expanding on previously developed PØD selections, new selections have been developed to select neutrino and antineutrino events in one and multiple track topologies on water and carbon. These selections are shown to have similar sensitivity to the T2K flux and cross section systematic uncertainties. Using the same parameterization as the official ND constraint result, a hypothesis test was conducted between the PØD-only and FGD-only data fit results. A p-value of 0.2865 was obtained indicating the two data sets are likely describing the same population of neutrinos and their interactions in T2K.
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    Massive neutrinos and the see saw mechanism
    (Colorado State University. Libraries, 2014) Campbell, Thomas, author; Toki, Walter, advisor; Buchanan, Norm, committee member; Biedron, Sandra, committee member
    In the current standard model of particle physics, neutrinos are massless and strictly left-chiral. With neutrino oscillations definitively observed, we know experimentally that neutrinos have non-zero mass. The standard model for leptons, including the Higgs mechanism for mass generation will be explored. Extensions to the standard model to give neutrinos mass and the so called see-saw mechanism will then be presented. Finally, one model of the see-saw mechanism purposed by S. F. King will then be compared to recent data from the T2K experiment.
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    Matter effects on neutrino oscillations
    (Colorado State University. Libraries, 2013) Gordon, Michael, author; Toki, Walter, advisor; Wilson, Robert, committee member; Estep, Donald, committee member
    An introduction to neutrino oscillations in vacuum is presented, followed by a survey of various techniques for obtaining either exact or approximate expressions for νμ→ νe oscillations in matter. The method developed by Arafune, Koike, and Sato uses a perturbative analysis to find an approximation for the evolution operator. The method used by Freund yields an approximate oscillation probability by diagonalizing the Hamiltonian, finding the eigenvalues and eigenvectors, and then using those to find modified mixing angles with the matter effect taken into account. The method devised by Mann, Kafka, Schneps, and Altinok produces an exact expression for the oscillation by determining explicitly the evolution operator. These methods are compared to each other using the T2K, MINOS, NOνA, and LBNE parameters.
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    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 member
    The 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.
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    Measurement of νμ induced charged current inclusive cross section on water using the near detector of the T2K experiment
    (Colorado State University. Libraries, 2016) Das, Rajarshi, author; Toki, Walter, advisor; Wilson, Robert, committee member; Berger, Bruce, committee member; Menoni, Carmen, committee member
    The Tokai to Kamioka (T2K) Experiment is a long-baseline neutrino oscillation experiment located in Japan with the primary goal to measure precisely multiple neutrino flavor oscillation parameters. An off-axis muon neutrino beam peaking at 600 MeV is generated at the JPARC facility and directed towards the 50 kiloton Super-Kamiokande (SK) water Cherenkov detector located 295 km away. Measurements from a Near Detector that is 280m downstream of the neutrino beam target are used to constrain uncertainties in the beam flux prediction and neutrino interaction rates. We present a selection of inclusive charged current neutrino interactions on water. We used several sub-detectors in the ND280 complex, including a Pi-Zero detector (P0D) that has alternating planes of plastic scintillator and water bag layers, a time projection chamber (TPC) and fine-grained detector (FGD) to detect and reconstruct muons from neutrino charged current events. We use a statistical subtraction method with the water-in and water-out inclusive selection to extract a flux-averaged, νμ induced, charged current inclusive cross section. We also outline the evaluation of systematic uncertainties. We find an absolute cross section of ⟨σ⟩Φ = (6.37 ± 0.157(stat.) (−1.060/+0.910(sys.)) × 10−39 (cm2/H2O nucleon). This is the first νμ charged current inclusive cross section measurement on water.