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Scholarly Works (4 results)

  • Thesis
  • Peer Reviewed
UC Berkeley Electronic Theses and Dissertations (2017)

At the IceCube Neutrino Observatory, neutrino interactions are observed across a broad energy range extending from ~ 5 GeV to ~ 1 PeV. Above ~ 100 TeV, neutrinos primarily originate from distant astrophysical objects whose identity is yet unknown. At lower energies, most neutrinos result from cosmic-ray interactions in Earth's atmosphere. In this work, two studies of contained neutrino interactions in IceCube are presented.

In the first study, three years of IceCube data recorded from May 2010 to May 2013 are analyzed to measure the flavor composition of astrophysical neutrinos in the energy range from 35 TeV to 1.9 PeV. The flavor composition is found to be consistent with the ratio of ~ (1/3 : 1/3 : 1/3) expected from the oscillation of neutrinos produced by complete pion decay in distant astrophysical sources. Limits are placed on non-standard flavor compositions that could arise in exotic physics scenarios. The energy spectrum of astrophysical neutrinos is also measured and is well-described by a falling power law with index 2.6+-0.15.

In the second study, five years of IceCube data from May 2011 to May 2016 are analyzed with improved background rejection and event classification techniques, and the inelasticity in charged-current muon neutrino interactions is reconstructed. Improved limits on the flavor composition of astrophysical neutrinos are obtained, and there is consistency with the expected flavor ratio of ~ (1/3 : 1/3 : 1/3). Additionally, the energy spectrum of astrophysical neutrinos is found to be consistent with a power-law with index 2.62+-0.07 in the energy range from 6.6 TeV to 2.2 PeV. Limits are placed on a power-law flux from a second population of astrophysical sources that may explain the harder power-law index of 2.13+-0.13 found in an IceCube analysis of up-going muons at higher energies.

The inelasticity distribution of charged-current muon neutrino interactions is also obtained and is found to be consistent with the calculation of Cooper-Sarkar et al. across an energy range from 1 TeV to 100 TeV. The inelasticity distribution can also be used measure the neutrino to antineutrino ratio of the atmospheric neutrino flux. A scaling factor on the muon neutrino to antineutrino flux ratio calculated by Honda et al. is found to be 0.77+0.44-0.25 in the energy range from 770 GeV to 21 TeV. Lastly, the inelasticity distribution can also be used to perform an indirect search for charged-current charm production by neutrinos. Assuming a leading-order calculation of the inelasticity distribution for charm production events, zero charm production can be excluded at 91% confidence level in the energy range from 1.5 TeV to 340 TeV. In the future, it is expected that the techniques developed for this analysis can be applied to search for neutrino interactions beyond the Standard Model in IceCube and next-generation neutrino telescopes.

    Cover page: Measurements of the Flavor Composition and Inelasticity Distribution of High-Energy Neutrino Interactions in IceCube
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2023)
    Background Many patients with heart failure (HF) have severely reduced ejection fraction but do not meet threshold for consideration of advanced therapies (ie, stage D HF). The clinical profile and health care costs associated with these patients in US practice is not well described. Methods and Results We examined patients hospitalized for worsening chronic heart failure with reduced ejection fraction ≤40% from 2014 to 2019 in the GWTG-HF (Get With The Guidelines-Heart Failure) registry, who did not receive advanced HF therapies or have end-stage kidney disease. Patients with severely reduced EF defined as EF ≤30% were compared with those with EF 31% to 40% in terms of clinical profile and guideline-directed medical therapy. Among Medicare beneficiaries, postdischarge outcomes and health care expenditure were compared. Among 113 348 patients with EF ≤40%, 69% (78 589) had an EF ≤30%. Patients with severely reduced EF ≤30% tended to be younger and were more likely to be Black. Patients with EF ≤30% also tended to have fewer comorbidities and were more likely to be prescribed guideline-directed medical therapy ("triple therapy" 28.3% versus 18.2%, P<0.001). At 12-months postdischarge, patients with EF ≤30% had significantly higher risk of death (HR, 1.13 [95% CI, 1.08-1.18]) and HF hospitalization (HR, 1.14 [95% CI, 1.09-1.19]), with similar risk of all-cause hospitalizations. Health care expenditures were numerically higher for patients with EF ≤30% (median US$22 648 versus $21 392, P=0.11). Conclusions Among patients hospitalized for worsening chronic heart failure with reduced ejection fraction in US clinical practice, most patients have severely reduced EF ≤30%. Despite younger age and modestly higher use of guideline-directed medical therapy at discharge, patients with severely reduced EF face heightened postdischarge risk of death and HF hospitalization.
      Cover page: Clinical Profile, Health Care Costs, and Outcomes of Patients Hospitalized for Heart Failure With Severely Reduced Ejection Fraction
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2024)
      The IceCube Neutrino Observatory instruments about 1ĝ€¯km3 of deep, glacial ice at the geographic South Pole. It uses 5160 photomultipliers to detect Cherenkov light emitted by charged relativistic particles. An unexpected light propagation effect observed by the experiment is an anisotropic attenuation, which is aligned with the local flow direction of the ice. We examine birefringent light propagation through the polycrystalline ice microstructure as a possible explanation for this effect. The predictions of a first-principles model developed for this purpose, in particular curved light trajectories resulting from asymmetric diffusion, provide a qualitatively good match to the main features of the data. This in turn allows us to deduce ice crystal properties. Since the wavelength of the detected light is short compared to the crystal size, these crystal properties include not only the crystal orientation fabric, but also the average crystal size and shape, as a function of depth. By adding small empirical corrections to this first-principles model, a quantitatively accurate description of the optical properties of the IceCube glacial ice is obtained. In this paper, we present the experimental signature of ice optical anisotropy observed in IceCube light-emitting diode (LED) calibration data, the theory and parameterization of the birefringence effect, the fitting procedures of these parameterizations to experimental data, and the inferred crystal properties.
        Cover page: In situ estimation of ice crystal properties at the South Pole using LED calibration data from the IceCube Neutrino ObservatoryCreative Commons 'BY' version 4.0 license
        • Article
        • Peer Reviewed
        UCLA Previously Published Works (2018)
        Previous detections of individual astrophysical sources of neutrinos are limited to the Sun and the supernova 1987A, whereas the origins of the diffuse flux of high-energy cosmic neutrinos remain unidentified. On 22 September 2017, we detected a high-energy neutrino, IceCube-170922A, with an energy of ~290 tera-electron volts. Its arrival direction was consistent with the location of a known γ-ray blazar, TXS 0506+056, observed to be in a flaring state. An extensive multiwavelength campaign followed, ranging from radio frequencies to γ-rays. These observations characterize the variability and energetics of the blazar and include the detection of TXS 0506+056 in very-high-energy γ-rays. This observation of a neutrino in spatial coincidence with a γ-ray-emitting blazar during an active phase suggests that blazars may be a source of high-energy neutrinos.
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