Physics
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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 Measurement of the W Boson Mass and Width Using a Novel Recoil Model(2009) Wetstein, Matthew Joseph; Eno, Sarah C; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation presents a direct measurement of the W boson mass (M_W) and decay width (&Gamma_W) in 1 fb^(-1) of W &rarr e &nu$ collider data at D0 using a novel method to model the hadronic recoil. The mass is extracted from fits to the transverse mass M_T, p_T(e), and MET distributions. The width is extracted from fits to the tail of the M_T distribution. The electron energy measurement is simulated using a parameterized model, and the recoil is modeled using a new technique by which Z recoils are chosen from a data library to match the p_T and direction of each generated W boson. We measure the the W boson mass to be M_W = 80.4035 ± 0.024 (stat) ± 0.039 (syst) from the M_T, M_W = 80.4165 ± 0.027 (stat) ± 0.038 (syst) from the p_T(e), and M_W = 80.4025 ± 0.023 (stat) ± 0.043 (syst) from the MET distributions. &Gamma_W is measured to be &Gamma_W=2.025 ± 0.038 (stat) ± 0.061 (syst)$ GeV.Item The Search for Neutralino Dark Matter with the AMANDA Neutrino Telescope(2008) Ehrlich, Ralf; Sullivan, Gregory; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)There is convincing indirect evidence based on cosmological data that approximately one quarter of the universe is made of dark matter. However, to this date there is no direct detection of the dark matter and its nature is unknown. Most theories suggest that this dark matter is made of Weakly Interacting Massive Particles (WIMPs), or more specifically: supersymmetric particles. The most promising candidate out of the supersymmetric particles is the lightest neutralino. These neutralinos can get trapped in the gravitational field of the Earth, where they accumulate and annihilate. The annihilation products decay and produce neutrinos (among other particles). These neutrinos (the focus is on muon-neutrinos here) can be detected with the AMANDA neutrino telescope located between one and two kilometers deep in the ice of the glacier near the South Pole. Neutrinos cannot be detected directly. However, there is a small possibility that they interact with nuclei of the ice and create charged leptons. These charged leptons continue to travel in the same direction as the neutrinos (accompanied by electromagnetic/hadronic cascades, and electrons). As long as their speed is higher than the speed of light of the ice, they emit Cherenkov radiation which can be captured by photomultipliers installed inside the ice. The signals collected by the photomultipliers can be used to reconstruct the track of the lepton. AMANDA - the Antarctic Muon and Neutrino Detector Array - makes use of the unique properties of the neutrino: Since neutrinos interact only weakly, they can travel through the Earth without being stopped. Therefore all detected particles which have been identified as upward going (i.e. through the Earth coming) must have been produced by charged leptons originating from neutrinos after they reacted with the nuclei of the ice. All other particles which do not come from below are rejected. If the neutrino flux coming from the neutralino annihilation inside Earth is strong enough to be detected with AMANDA, it should show up as an excess over the expected neutrino flux, which comes from the atmospheric neutrinos produced in the northern hemisphere. This analysis which used data from 2001 and 2002 showed that there is no significant excess, yielding an upper limit on the neutrino flux that could have come from WIMP annihilation.Item Radiative B Meson Decay as a Probe of Physics Beyond the Standard Model: Time-Dependent CP Violation in B0 → KS π0 γ and the B → φ K γ Branching Fraction(2008) Tuggle, Joseph M.; Jawahery, Abolhassan; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)I present measurements of radiative B meson decays to the final states KS π0 γ and K φ γ based on data collected at the Υ(4S) resonance with the BaBar detector at the PEP-II e+e– collider at SLAC. In a data sample of 467 million BBbar pairs, the time-dependent CP asymmetry in B0 → KS π0 γ decays is measured in two regions of KS-π0 invariant mass. In the K* region, 0.8 < m(KS π0) < 1.0 GeV/c2, we find SK* γ = –0.03 ± 0.29 ± 0.03 and CK* γ = –0.14 ± 0.16 ± 0.03; in the range 1.1 < m(KS π0) < 1.8 GeV/c2, we find SKS π0 γ = –0.78 ± 0.59 ± 0.09 and CKS π0 γ = –0.36 ± 0.33 ± 0.04. With a sample of 228 million BBbar pairs we measure the branching fraction B(B+ → K+ φ γ) = (3.5 ± 0.6 ± 0.4) × 10–6 and set the limit B(B0 → K0 φ γ) < 2.7 × 10–6 at 90% confidence level. The direct CP asymmetry in B+ → K+ φ γ is found to be ACP = (–26 ± 14 ± 5)%. In each case the uncertainties are statistical and systematic, respectively.Item Meaurement of CP content and time-dependent CP violation in B0 → D*+D*- decays(2008) Anderson, Jacob M.; Roberts, Douglas; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation presents the measurement of the the CP-odd fraction and time-dependent CP violation parameters for the B0 → D*+D*- decay. These results are based on the full BaBar dataset of (467 ± 5) × 106 BB pairs collected at the PEP-II B factory at the Stanford Linear Accelerator Center. An angular analysis finds that the CP-odd fraction of the B0 → D*+D*- decay is R⊥ = 0.158 ± 0.028 ± 0.006, where the first uncertainty is statistical, and the second is systematic. A fit to the flavor-tagged, time-dependent, angular decay rate yields
C+ = 0.02 ± 0.12 ± 0.02
C⊥ = 0.41 ± 0.50 ± 0.08
S+ = -0.76 ± 0.16 ± 0.04
S⊥ = -1.81 ± 0.71 ± 0.16,
for the CP-odd (⊥) and CP-even (+) contributions. Constraining these two contributions to be the same results in
C = 0.047 ± 0.091 ± 0.019
S = -0.71 $plusmn; 0.16 ± 0.03.
These measurements are consistent with the Standard Model and with measurements of sin2β from B0 → (cc)K0 decays.Item Vacuum Properties of QCD in an Electromagnetic Field(2009) Werbos, Elizabeth; Cohen, Thomas D; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The non-trivial vacuum properties of Quantum Chromodynamics can be affected by a constant external magnetic field. The chiral condensate and the magnetization of the vacuum are the two properties studied in this work. The chiral condensate, which is the order parameter for chiral symmetry breaking--one of the most important properties of QCD--is an optimal quantity to study at intermediate field strengths. Using both models and chiral perturbation theory, it can be shown that an electric field suppresses the chiral condensate whereas a magnetic field enhances it. Higher-order calculations in χPT may have a substantial effect on the magnitude of the shift in the chiral condensate, but their exact effect is unknown due to the uncertainty in the parameters of the theory. The second parameter, the magnetization, is used at fields large enough for perturbative calculations to be valid; at these scales, there is large explicit chiral symmetry breaking and the chiral condensate cannot be used. The first-order magnetization shows a correction of the form B log B; the calculation to next order in perturbation theory shows a correction small enough that non-perturbative corrections dominate.Item A Blind Search for Bursts of Very High Energy Gamma Rays with Milagro(2008-08-03) Vasileiou, Vlasios; Goodman, Jordan A; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Milagro is a water-Cherenkov detector that observes the extended air showers produced by cosmic gamma rays of energies E>100GeV. The effective area of Milagro peaks at energies E>10TeV, however it is still large even down to a few hundred GeV (~10m^2 at 100GeV). The wide field of view (~2sr) and high duty cycle (>90%) of Milagro make it ideal for continuously monitoring the overhead sky for transient Very High Energy (VHE) emissions. This study searched the Milagro data for such emissions. Even though the search was optimized primarily for detecting the emission from Gamma-Ray Bursts (GRBs), it was still sensitive to the emission from the last stages of the evaporation of Primordial Black Holes (PBHs) or to any other kind of phenomena that produce bursts of VHE gamma rays. Measurements of the GRB spectra by satellites up to few tens of GeV showed no signs of a cutoff. Even though multiple instruments sensitive to GeV/TeV gamma rays have performed observations of GRBs, there has not yet been a definitive detection of such an emission yet. One of the reasons for that is that gamma rays with energies E>100GeV are attenuated by interactions with the extragalactic background light or are absorbed internally at the site of the burst. There are many models that predict VHE gamma-ray emission from GRBs. A detection or a constraint of such an emission can provide useful information on the mechanism and environment of GRBs. This study performed a blind search of the Milagro data of the last five years for bursts of VHE gamma rays with durations ranging from 100 micro seconds to 316 seconds. No GRB localization was provided by an external instrument. Instead, the whole dataset was thoroughly searched in time, space, and duration. No significant events were detected. Upper limits were placed on the VHE emission from GRBs.Item The upside of minimal left-right supersymmetric seesaw in deflected anomaly mediation(2008-05-30) Spinner, Sogee; Mohapatra, Rabindra; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The state of the standard model of particle physics is reviewed focusing on two of it's major issues: the hierarchy problem and its inconsistency with observed neutrino masses. Supersymmetry, an elegant solution to the former, and the seesaw mechanism in left-right models, a natural solution to the latter, are then introduced. The work then focuses on a specific supersymmetric left-right models, which has an additional discrete symmetry allowing a prediction of the seesaw scale at around 1011 GeV--consistent with neutrino oscillation data. It also solves the μ problem and guarantees automatic R-parity conservation and a pair of light doubly-charged Higgses which can be searched for at the LHC. This model has interesting properties in the context of anomaly mediated supersymmetry breaking (AMSB). After a brief introduction to this topic, it is shown that this model is an instance of the Pomarol Rattazzi model of deflected AMSB. The tachyonic slepton problem of AMSB is solved in a combination of two ways: the right-handed sleptons are saved by their couplings to the low energy doubly-charged fields while the left-handed sleptons receive positive contributions from the partially decoupled D-terms. The resulting phenomenology is similar to that of mimimal AMSB due to the gaugino spectrum; however, same generation mass differences in the sfermion sector are much larger than that of mAMSB and the right-handed selectron can be as massive as the squarks. Finally, this model also contains a mechanism for solving the EWSB problem of AMSB and a dark matter candidate.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.Item APPLYING NUMERICAL RELATIVITY TO GRAVITATIONAL WAVE ASTRONOMY(2008-03-12) McWilliams, Sean Thomas; Shawhan, Peter; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)General relativity predicts the existence of gravitational waves produced by the motion of massive objects. The inspiral, merger, and ringdown of black hole binaries is expected to be one of the brightest sources in the gravitational wave sky. Interferometric detectors, such as the current ground-based Laser Interferometer Gravitational Wave Observatory (LIGO) and the future space-based Laser Interferometer Space Antenna (LISA), measure the influx of gravitational radiation from the whole sky. Each physical process that emits gravitational radiation will have a unique waveform, and prior knowledge of these waveforms is needed to distinguish a signal from the noise inherent in the interferometer. In the strong field regime of the merger, only numerical relativity, which solves the full set of Einstein's equations numerically, has been able to provide accurate waveforms. We present a comprehensive study of the nonspinning portion of parameter space for which we have generated accurate simulations of the late inspiral through merger and ringdown, and a comparison of those results with predictions from the adiabatic Taylor-expanded post-Newtonian (PN) and effective-one-body (EOB) PN approximations. We then focus on data analysis questions using the equal-mass nonspinning as well as the 2:1, 4:1, and 6:1 mass ratio nonspinning black hole binary (BHB) waveforms. We construct a full waveform by combining our results from numerical relativity with a highly accurate Taylor PN approximation, and use it to calculate signal-to-noise ratios (SNRs) for several detectors. We measure the mass ratio scaling of the waveform amplitude through the inspiral and merger, and compare our observations with predictions from PN. Lastly, we turn our focus to parameter estimation with LISA, and investigate the increased accuracy with which parameters can be measured by including both the merger and inspiral waveforms, compared to estimates without numerical waveforms which can only incorporate the inspiral. We use the equal mass, nonspinning waveform as a test case and assess the parameter uncertainty by means of the Fisher matrix formalism.