Browsing by Author "Berger, Bruce, committee member"
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Item Open Access 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 memberThe 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.Item Open Access Barium tagging in solid xenon for the EXO experiment(Colorado State University. Libraries, 2011) Mong, Brian, author; Fairbank, William, Jr., advisor; Lundeen, Stephen, committee member; Berger, Bruce, committee member; Van Orden, Alan, committee memberNeutrinoless double beta decay experiments are searching for rare decay modes never before observed to uncover the absolute mass of the neutrino, as well as to discover if it is a Majorana fermion. Detection of the daughter nucleus can help provide positive identification of this event over most radioactive backgrounds. The goal of the Enriched Xenon Observatory (EXO) is to measure the rate of 0νββ decay in 136Xe, incorporating 136Ba daughter identification by laser induced fluorescence spectroscopy. Here, we investigate a technique in which the 136Ba daughter is grabbed with a cryogenic probe by freezing it in solid xenon ice, and detected directly in the solid xenon. The absorption and fluorescence spectra of barium in solid xenon were observed for the first time in this work. Identification of the 6s2 1S0 → 6s6p 1P1 transition in both absorption (558 nm) and emission spectra (594 nm) were made. Additional blue absorption and emission lines were observed, but their transitions were not identified. Saturation of the 6s2 1S0 → 6s6p 1P1 transition was not observed with increased excitation rates using resonance excitation at 558 nm. From this a limit on the metastable decay rate was deduced to be greater than 104 s-1. Finally a fluorescence spectrum was obtained from a sample with only 20,000 atoms in the laser beam. With potential improvements of 107 in detection efficiency, single barium atom detection seems possible in solid xenon. A fiber probe detector based on a bare single mode fiber was also constructed and tested with fluorescing dye molecules. Successful detection of a few dye molecules in solution at the probe tip was demonstrated.Item Open Access Constraints on the galactic magnetic field with two-point cumulative autocorrelation function(Colorado State University. Libraries, 2012) Petrov, Yevgeniy, author; Harton, John L., advisor; Mostafá, Miguel A., committee member; Berger, Bruce, committee member; Burns, Patrick J., committee memberThe fact that ultra high energy cosmic rays are charged particles complicates identication of their sources due to deflections by the intervening cosmic magnetic fields. The information about the fields is encoded in the amount of deflection experienced by a charged particle. Unfortunately, the positions of sources are unknown as is the structure of the magnetic field. However, it is possible to deduce the most favorable galactic magnetic field by examining the parameter space of different models of the galactic magnetic field. The method presented in this work is valid under some plausible assumptions, such as extragalactic origin of the UHECR, pure protonic composition above 50 EeV and sufficiently weak randomly oriented galactic and extragalactic components of the magnetic field. I use a two point cumulative autocorrelation function combined with the backtracking method to find regions in the parameter space that are compatible with statistically significant clustering on the extragalactic sky. This approach is independent of any catalog of sources. The ratio between the number of pairs within a certain angular window at the Earth sky and at the extragalactic sky after backtracking serves to indicate focusing or de-focusing properties of a particular field configuration. The results suggest that among several tested fields, the Harari-Mollerach-Roulet model with a bi-symmetric spiral and even vertical symmetry favors clustering of arrival directions at the extragalactic sky with the probability of 2.5% being from an isotropic distribution. Addition of the toroidal halo field improves clustering for the Harari-Mollerach-Roulet field for both bi-symmetric and axisymmetric spirals with even vertical symmetry, and the isotropic probabilities are 2.5% and 5.3% correspondingly. The bi-symmetric and axisymmetric spirals with odd vertical symmetry are disfavored, as well as the models with annular structure.Item Open Access Group action on neighborhood complexes of Cayley graphs(Colorado State University. Libraries, 2014) Hughes, Justin, author; Hulpke, Alexander, advisor; Peterson, Chris, advisor; Berger, Bruce, committee member; Cavalieri, Renzo, committee member; Wilson, James, committee memberGiven G a group generated by S ≐ {g1, …, gn}, one can construct the Cayley Graph Cayley (G,S). Given a distance set D ⊂ Z≥0 and Cayley (G,S) one can construct a D-neighborhood complex. This neighborhood complex is a simplicial complex to which we can associate a chain complex. The group G acts on this chain complex and this leads to an action on the homology of the chain complex. These group actions decompose into several representations of G. This thesis uses tools from group theory, representation theory, homo-logical algebra, and topology to further our understanding of the interplay between generated groups (i.e. a group together with a set of generators), corresponding representations on their associated D-neighborhood complexes, and the homology of the D-neighborhood complexes.Item Open Access Imaging single barium atoms in solid xenon for barium tagging in the nEXO neutrinoless double beta decay experiment(Colorado State University. Libraries, 2016) Walton, Timothy, author; Fairbank, William M., advisor; Berger, Bruce, committee member; Van Orden, Alan, committee member; Wilson, Robert, committee memberThe nEXO experiment will search for neutrinoless double beta decay of the isotope 136Xe in a ton-scale liquid xenon time projection chamber, in order to probe the Majorana nature of neutrinos. Detecting the daughter 136Ba of double beta decay events, called barium tagging, is a technique under investigation which would provide a veto for a background-free measurement. This would involve detecting a single barium ion from within a macroscopic volume of liquid xenon. One proposed barium tagging method is to trap the barium ion in solid xenon at the end of a cold probe, and then detect it by its fluorescence in the solid xenon. In this thesis, new studies on the spectroscopy of deposits of Ba and Ba+ in solid xenon are presented. Imaging of barium atoms in solid xenon is demonstrated with sensitivity down to the single atom level. Achievement of this level of sensitivity is a major step toward barium tagging by this method.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 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 memberThe 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.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 Mobility and fluorescence of barium ions in xenon gas for the EXO experiment(Colorado State University. Libraries, 2014) Benitez Medina, Julio Cesar, author; Fairbank, William, advisor; Berger, Bruce, committee member; Lundeen, Stephen, committee member; Menoni, Carmen, committee memberThe Enriched Xenon Observatory (EXO) is an experiment which aims to observe the neutrinoless double beta decay of 136Xe. The measurement of this decay would give information about the absolute neutrino mass and whether or not the neutrino is its own antiparticle. Since this is a very rare decay, the ability to reject background events by detecting the barium ion daughter from the double beta decay would be a major advantage. EXO is currently operating a detector with 200 kg of enriched liquid xenon, and there are plans to build a ton scale xenon detector. Measurements of the purity of liquid xenon in our liquid xenon test cell are reported. These results are relevant to the research on detection of single barium ions by our research group at Colorado State University. Details of the operation of the purity monitor are described. The effects of using a purifier, recirculation and laser ablation on the purity of liquid xenon are discussed. Mobility measurements of barium in xenon gas are reported for the first time. The variation of mobility with xenon gas pressure suggests that a significant fraction of molecular ions are formed when barium ions interact with xenon gas at high pressures. The measured mobility of Ba+ in Xe gas at different pressures is compared with the predicted theoretical value, and deviations are explained by a model that describes the fraction of molecular ions in Xe gas as a function of pressure. The results are useful for the analysis of experiments of fluorescence of Ba+ in xenon gas. It is also important to know the mobility of the ions in order to calculate the time they interact with an excitation laser in fluorescence experiments and in proposed 136Ba+ daughter detection schemes. This thesis presents results of detection of laser induced fluorescence of Ba+ ions in Xe gas. Measurements of the pressure broadening of the excitation spectra of Ba+ in xenon gas are presented. Nonradiative decays due to gas collisions and optical pumping affect the number of fluorescence counts detected. A model that treats the barium ion as a three level system is used to predict the total number of fluorescence counts and correct for optical pumping. A pressure broadening coefficient for Ba+ in xenon gas is extracted and limits for p-d and d-s nonradiative decay rates are extracted. Although fluorescence is reduced significantly at 5-10 atm xenon pressure, the measurements in this thesis indicate that it is still feasible to detect 136Ba+ ions directly in high pressure xenon gas, e.g. in a double beta decay detector.