Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item An All-Sky, Three-Flavor Search for Neutrinos from Gamma-Ray Bursts with the IceCube Neutrino Observatory(2015) Hellauer, Robert Eugene; Sullivan, Gregory; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Ultra high energy cosmic rays (UHECRs), defined by energy greater than 10^18 eV, have been observed for decades, but their sources remain unknown. Protons and heavy ions, which comprise cosmic rays, interact with galactic and intergalactic magnetic fields and, consequently, do not point back to their sources upon measurement. Neutrinos, which are inevitably produced in photohadronic interactions, travel unimpeded through the universe and disclose the directions of their sources. Among the most plausible candidates for the origins of UHECRs is a class of astrophysical phenomena known as gamma-ray bursts (GRBs). GRBs are the most violent and energetic events witnessed in the observable universe. The IceCube Neutrino Observatory, located in the glacial ice 1450 m to 2450 m below the South Pole surface, is the largest neutrino detector in operation. IceCube detects charged particles, such as those emitted in high energy neutrino interactions in the ice, by the Cherenkov light radiated by these particles. The measurement of neutrinos of 100 TeV energy or greater in IceCube correlated with gamma-ray photons from GRBs, measured by spacecraft detectors, would provide evidence of hadronic interaction in these powerful phenomena and confirm their role in ultra high energy cosmic ray production. This work presents the first IceCube GRB-neutrino coincidence search optimized for charged-current interactions of electron and tau neutrinos as well as neutral-current interactions of all neutrino flavors, which produce nearly spherical Cherenkov light showers in the ice. These results for three years of data are combined with the results of previous searches over four years of data optimized for charged-current muon neutrino interactions, which produce extended Cherenkov light tracks. Several low significance events correlated with GRBs were detected, but are consistent with the background expectation from atmospheric muons and neutrinos. The combined results produce limits that place the strongest constraints thus far on models of neutrino and UHECR production in GRB fireballs.Item Proton and Helium Spectra from the First Flight of the CREAM Balloon-Borne Experiment(2010) Yoon, Young Soo; Seo, EunSuk; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Cosmic-ray proton and helium spectra have been measured with the balloon-borne Cosmic Ray Energetics And Mass (CREAM) experiment flown for 42 days in Antarctica in the 2004-2005 austral summer season. High-energy cosmic-ray data were collected at an average altitude of ∼38.5 km with an average atmospheric overburden of ∼3.9 g/cm2. Individual elements are clearly separated with a charge resolution of ∼0.15e (in charge units) and ∼0.2e, respectively, for protons and helium nuclei. The measured spectra at the top of the atmosphere are represented by a power law with a spectral index of -2.66 ± 0.02 for protons from 2.5 TeV to 250 TeV and -2.58 ± 0.02 for helium nuclei from 630 GeV/nucleon to 63 TeV/nucleon. The measured proton and helium spectra are harder than previous measurements at a few tens of GeV/nucleon. Possible explanations of this spectral hardening could be the effect of a relatively nearby source or the effect of spectral concavity caused by interactions of cosmic rays with the accelerating shock. The helium flux is higher than that expected from extrapolation of a power-law fit to the lower-energy data. The relative abundance of protons to helium nuclei is about 8.8 ± 0.5 in the range from 2.5 TeV/nucleon to 63 TeV/nucleon. In this thesis, the analysis of proton and helium spectra will be discussed.Item Search for Quantum Gravity with IceCube and High Energy Atmospheric Neutrinos(2010) Huelsnitz, Warren; Hoffman, Kara; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)IceCube is a cubic-kilometer neutrino telescope nearing completion in the South Pole Ice. Designed to detect astrophysical neutrinos from 100 GeV to about an EeV, it will contribute to the fields of high energy astrophysics, particle physics, and neutrino physics. This analysis looks at the flux of atmospheric neutrinos detected by IceCube while it operated in a partially-completed, 40-string configuration, from April 2008 to May 2009. From this data set, a sample of about 20,000 up-going atmospheric muon neutrino events with negligible background was extracted using Boosted Decision Trees. A discrete Fourier transform method was used to constrain a directional asymmetry in right ascension. Constraints on certain interaction coefficients from the Standard Model Extension were improved by three orders of magnitude, relative to prior experiments. The event sample was also used to unfold the atmospheric neutrino spectrum at its point of origin, and seasonal and systematic variations in the atmospheric muon neutrino flux were studied. A likelihood method was developed to constrain perturbations to the energy and zenith angle dependence of the atmospheric muon neutrino flux that could be due to Lorentz-violating oscillations or decoherence of neutrino flavor. Such deviations could be a signature of quantum gravity in the neutrino sector. The impact of systematic uncertainties in the neutrino flux and in the detector response on such a likelihood analysis were examined. Systematic uncertainties that need to be reduced in order to use a two-dimensional likelihood analysis to constrain phenomenological models for Lorentz or CPT violating neutrino oscillations were identified.