Theses and Dissertations from UMD
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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 A Search For Muon Neutrinos Coincident With Gamma-Ray Bursts Using IceCube(2015) Richman, Michael David; Hoffman, Kara; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)We present constraints derived from a search of four years of IceCube data for a prompt neutrino flux from gamma-ray bursts (GRBs). A single low-significance neutrino was found in coincidence with one of the 506 observed bursts, consistent with the expectation from atmospheric backgrounds. Although GRBs have been proposed as candidate sources for ultra-high energy cosmic rays, our limits on the neutrino flux disfavor much of the parameter space for the latest models. We also find that no more than ~1% of the recently observed astrophysical neutrino flux consists of prompt emission from GRBs that are potentially observable by existing satellites. These results currently represent world-leading constraints on a prompt neutrino flux from GRBs. In this thesis, we also introduce an original machine learning software package called pybdt. This implementation is now the de facto standard tool for machine-learning-based classification in IceCube analyses. Finally, we describe an extension of the unbinned likelihood method used in past searches to allow for the combination of data from different detector configurations with different background characteristics in the calculation of model constraints.Item A Search for the Neutrinoless Double Beta Decay of Xenon-136 with Improved Sensitivity from Denoising(2014) Davis, Clayton G.; Hall, Carter; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The EXO-200 detector is designed to search for the neutrinoless double beta decay of 136Xe. ββ0ν decay, if it occurs in nature, would demonstrate the fundamental nature of neutrino mass; set the mass scale of the neutrino sector; and demonstrate lepton number non-conservation. Since the ββ0ν decay produces a monoenergetic peak, the energy resolution of the detector is of fundamental importance for the sensitivity of the experiment. The present work describes a new analysis technique which improves the energy resolution of EXO-200 through a combination of waveform denoising and weighting of waveform components based on their expected signal-to-noise ratio. With this method, the energy resolution of the detector is improved by 21% and the expected background in the 2σ region of interest is reduced by 32%. Applying this technique to 99.8 kg*years of exposure collected by EXO-200 between October 5, 2011 and September 1, 2013, we find no statistically significant evidence for the presence of ββ0ν in the data. We set a half-life limit T1/2 > 1.1 × 1025 years at 90% confidence. We also describe further improvements which could impact the energy resolution of EXO-200, and consider implications for the planned nEXO experiment.Item A Search for the Double-Beta Decay of Xe-136 to an Excited State of Ba-136 with EXO-200(2013) Yen, Yung-Ruey; Hall, Carter R; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis presents a search for the two neutrino double beta decay (ββ2ν) of 136Xe to the 0+1 excited state of 136Ba using data from the EXO-200 detector collected between 2011 and 2012. The ββ2ν decay to the excited state is a process that have been observed for other double beta decay nuclei. An observation of this decay would shed some light on the validities of the various nuclear physics models. Located at the Waste Isolation Pilot Plant (WIPP) near Carlsbad, NM, EXO-200 is a liquid xenon time projection chamber filled with 200 kg of 80.6% isotopically enriched 136Xe. The liquid xenon serves both as the decay source and the detection medium. Maximum likelihood fits of the sum energy spectra based on Monte Carlo simulations are used to constrain the number of ββ2ν decay to the 0+1 excited state of 136Ba. A half-life lower limit on this decay of 1.2 · 1023 year at 90% C.L is set, still a couple orders of magnitude from our expected theoretical rate of 2.5 · 1025 year from the applying the calculated phase space factor and the nuclear matrix element suppressions on the measured ββ2ν decay to the ground state. A developing analysis using a new energy variable designed specifically for the search of the decay to the excited state is also discussed.Item A Search for Neutrinoless Double-Beta Decay with EXO-200(2013) Slutsky, Simon; Hall, Carter R.; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This work presents a search for neutrinoless double beta decay of 136Xe using data from the EXO-200 detector collected between 2011 and 2012. Neutrinoless double beta decay (ββ0ν) is a hypothetical nuclear decay possible only if the neutrino is massive and is a Majorana particle. Observation of this process would constitute a measurement of the absolute neutrino mass scale, which is known to be non-zero from neutrino oscillation experiments. EXO-200 is a liquid xenon time projection chamber located at the Waste Isolation Pilot Plant (WIPP) in Carlsbad, NM. The detector is filled with 200 kg of liquid xenon isotopically enriched to 80.6%, used as both detection medium and decay source. Spectral fits based on detailed Monte Carlo simulations are used to constrain the number of events in the data. The analysis finds no evidence for ββ0ν in 136Xe, placing a lower limit on the half-life of 1.6 ·1025 yr at 90% confidence level. This implies an upper limit on the effective Majorana neutrino mass between 0.14-0.38 eV, one of the most stringent limits ever set on ββ0ν.Item A search for muon neutrinos coincident with Gamma-ray Bursts with the IceCube 59-String detector(2011) Redl, Peter Christian; Sullivan, Gregory; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Gamma-Ray Bursts (GRBs) are believed to be prime candidates to produce the cosmic ray flux above 10^18 eV. Cosmic rays are deflected by galactic and inter-galactic magnetic fields and do not point back to their source, therefore cosmic ray observations cannot confirm or rule out GRBs as a source. Leading theories predict that if GRBs are indeed responsible for the highest energy cosmic rays, then they would produce a detectable TeV-scale neutrino flux in a km^3 sized neutrino detector. Neutrinos are not deflected by magnetic fields and point back to their source, making it possible to correlate a neutrino flux with its source. The detection of a neutrino flux from GRBs would be strong evidence that GRBs are a source of the highest energy cosmic rays. IceCube is the first km^3 sized neutrino detector in the world and is therefore sensitive to the predicted TeV neutrino flux from GRBs. The finished detector consists of 5160 light-sensitive Digital Optical Modules (DOM) arranged on 86 Strings. There are 60 DOMs on a single string deployed at depths between 1450 and 2450 meters below the surface. The first IceCube String was deployed during the South Pole summer of 2004-2005 with construction of the IceCube detector finishing during the austral summer of 2011. The results presented here are from the 59-string detector, which operated from May 2009 to May 2010. IceCube is able to detect charged particles moving through its instrumented volume near the speed of light by detecting the Cherenkov light given off by those charged particles. Muon and anti-muon neutrinos produce secondary muons if they interact with a nucleon. If this interaction happens in or near the instrumented volume IceCube can detect those secondary muons. By searching for a neutrino signal coincident in time and space with satellite detected gamma rays from GRBs, the analysis presented here pushes the sensitivity for neutrinos from GRBs to 0.46 times the theoretically predicted neutrino flux. The result is combined with the previous search and a combined 90% upper limit of 0.22 times the theoretical predicted flux is set. The implication of this stringent limit on the model is discussed and future IceCube sensitivities are outlined. IceCube is the largest neutrino detector in the world and with this result has entered the era of neutrino astrophysics by constraining long standing astrophysical neutrino production models.Item A Search for Muon Neutrinos from Gamma-Ray Bursts wih the IceCube 22-String Detector(2009) Roth, A Philip; Hoffman, Kara; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Two searches are conducted for muon neutrinos from Gamma-Ray Bursts (GRBs) using the IceCube detector. Gamma-Ray Bursts are brief and transient emissions of keV/MeV radiation occuring with a rate of a few per day uniformly in the sky. Swift and other satellites of the Third Interplanetary Network (IPN3) detect these GRBs and send notices out via the GRB Coordinate Network (GCN). The fireball model describing the physics of GRBs predicts the emission of muon neutrinos from these bursts. IceCube is a cubic kilometer neutrino detector buried in the deep antarctic ice at the South Pole that can be used to find these prediceted but still unobserved neutrinos. It is sensitive to them by detecting Cherenkov light from secondary muons produced when the neutrinos interact in or near the instrumented volume. The construction of IceCube has been underway since the austral summer of 2004-2005 and will continue until 2011. The growing IceCube detector will soon be sensitivite to the high energy neutrino emission from GRBs that is predicted by the fireball model. A blind and triggered search of the 22-string IceCube data for this neutrino emission was conducted. The principal background to the observation of neutrinos in IceCube is muons generated in cosmic-ray air-showers in the atmosphere above the detector. Atmospheric neutrinos make up a separate irreducible background to the detection of extraterrestrial neutrinos. A binned stacked search of 41 bursts occuring in the northern hemisphere greatly reduces the muon background by looking for tracks moving up through the detector. The atmospheric neutrino background is greatly reduced by the temporal constraints of the search, making it effectively background free. 40 individual unbinned searches of bursts occuring in the southern hemisphere extend IceCube's sensitivity to the higher background regions above the horizon. No significant excesses over background expectations are found in either search. A 90% confidence upper limit on the neutrino fluence from northern hemisphere bursts is set at 6.52 x 10-3 erg cm-2 with 90% of the expected signal between 87.9 TeV and 10.4 PeV.Item nu Seesaw Uses: UV Insensitive Supersymmetry Breaking without Tachyons(2008-06-04) Setzer, Nicholas; Mohapatra, Rabindra N; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This document contains a systematic analysis of supersymmetric left-right models in the context of anomaly mediated supersymmetry breaking starting with the high-scale, left-right theory and ending with the supersymmetry-scale theory. It is shown that the combination of supersymmetric left-right models and anomaly mediated supersymmetry breaking retains the attractive features of anomaly mediation while simultaneously providing a solution to the tachyonic slepton problem of the minimal supersymmetric standard model with anomaly mediated supersymmetry breaking. The supersymmetric left-right theory introduces new yukawa couplings that permit positive slepton mass-squares while retaining the ultra violet insensitivity of anomaly mediated supersymmetry breaking as well its economy. The new couplings are introduced by independent considerations of explaining neutrino oscillation experiments through the seesaw mechanism, and survive below the seesaw scale from an accidental symmetry of the potential. Furthermore, the seesaw mechanism is implemented in such a way that R-parity is a natural residual symmetry--leading to a stable, weakly-interacting particle to explain dark matter. The resulting mass spectrum is detailed, both qualitatively and quantitatively, providing comparisons with other popular supersymmetry breaking scenarios. It is demonstrated that the model contains gaugino masses that are much closer in size than other schemes, as well as the possibility of a mild squark-slepton mass degeneracy. The issue of higgsino masses is also explored, and attention is paid to the dark matter composition. The model is shown to have a viable dark matter candidate that evades current direct detection bounds but will be probed by future planned experiments. The low-energy consequences of the model are analyzed, and the matter of electroweak symmetry breaking is expounded. It is shown that the problem of a higgsino mass below the LEP II bound in the next-to minimal supersymmetric standard model with anomaly mediated supersymmetry breaking is easily avoided by this theory. Finally, prospects for confirmation of this theory at the LHC are investigated, as well as potential signatures in lepton flavor violation experiments.