Browsing by Subject "supernova"

Now showing 1 - 3 of 3
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    Astrophysics and Physics of Neutrino Detection
    (2017-09) Li, Cheng-Hsien
    A galactic core-collapse supernova is a powerful neutrino source of which the signals can be picked up by a water Cherenkov detector on the Earth. From an astrophysical point of view, the signals reveal the dynamics of core-collapse supernova explosion and the subsequent cooling of a proto-neutron star (PNS). In this regard, we compare the neutrino emission profiles from the recent 1D hydrodynamics simulation by Mirizzi et al. (2016) with the historical SN1987A data through a statistical goodness-of-fit test. Such test reveals the tension between the data and rapid PNS cooling prescribed by the convection treatment employed in the simulation. The implications will be discussed. From a quantum-mechanical point of view, on the other hand, the supernova neutrino flux is so intensive such that a huge degree of wave-packet overlap is estimated. Such overlap may give rise to an interference effect known as the Hanbury Brown and Twiss (HBT) effect. We derive the solution for a 3D Gaussian wave packet and, with such solution, the joint-detection probability. We demonstrate that an observable interference occurs if the joint-detection were to render the two detected neutrinos in the same phase space cell. Upon further examination, however, we conclude that such effect is difficult to observe from neutrinos in practical experimental settings.
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    Collective Neutrino Oscillations in Neutrino-Driven Winds
    (2020-12) Xiong, Zewei
    A proto-neutron star produced in a core-collapse supernova (CCSN) drives a wind by its intense neutrino emission. Those dense neutrino media can undergo various collective neutrino oscillations and exert feedback on the wind through neutrino absorptions and emissions. In this thesis, I study the effects of two collective oscillations: the active-sterile neutrino and fast flavor oscillations.I implement active-sterile neutrino oscillations in a steady-state model of this neutrino-driven wind to study their effects on the dynamics and nucleosynthesis of the wind in a self-consistent manner. For the higher mass values of a sterile neutrino on the eV scale, oscillations can reduce the mass loss rate and the wind velocity by factors of ~ 1.6–2.7 and change the electron fraction critical to nucleosynthesis by a large amount. In the most dramatic cases, oscillations shift nucleosynthesis from dominant production of 45Sc to that of 86Kr and 90Zr during the early epochs of the CCSN evolution. Active-sterile neutrino oscillations in the wind exhibit interesting features due to various feedbacks between the potentials from neutrino-electron and neutrino-neutrino forward scattering. These feedbacks were studied in detail. In addition, I study the effects of fast neutrino flavor oscillations on the νp process in neutrino driven winds. Using the unoscillated neutrino emission characteristics from two CCSN simulations representative of relevant progenitors at the lower and higher mass end, I study the potential effects of fast flavor oscillations on neutrino-driven winds and their nucleosynthesis. Such oscillations are found to increase the total mass loss by factors up to ~ 1.5–1.7 and lead to significantly more proton-rich conditions. The latter effect can greatly enhance the production of 64Zn and the so-called light p-nuclei 74Se, 78Kr, and 84Sr.
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    Studies of Core-Collapse Supernova Models Using Past and Future Neutrino Data
    (2022-01) Olsen, Jackson
    Core-collapse supernovae expel a large amount of energy through the emission of neutrinos. These neutrinos carry important information about the environment in and around the core of the star during the first seconds after core bounce has occurred and the supernova shock has been initiated. By detecting the neutrino signal from a supernova, observers on Earth could extract this information from the neutrinos. Typically, simulations are used to accurately model the neutrino emission, with the neutrino signal depending on the input physics of the simulation. In this thesis, I consider the feasibility of using core-collapse supernova neutrino data to distinguish between different simulated supernova models, which vary in both the progenitor mass and the high-density nuclear equation of state. I also study whether SN neutrinos could be used to determine the neutrino mass hierarchy. Neutrinos have been observed from one supernova, SN 1987A. Unfortunately, the sample size is not very large. In the first part of this thesis, I describe a Bayesian analysis using the limited SN 1987A neutrino data from the Kamiokande II detector to compare several supernova models. This analysis indicates that the data most favors a model with a lower mass progenitor, and a shorter accretion emission phase. I also present the results of a secondary, goodness-of-fit analysis to test for incompatibility between the data and the models. The goodness-of-fit analysis suggests that the data is incompatible with the predicted total number of events from a model with a long, pronounced accretion period. The Bayesian analysis of the SN 1987A data does not provide us with comprehensive, definitive conclusions, given the limited size of the data set. In the second part of this thesis, I consider the case in which a future Galactic supernova occurs, and a water Cherenkov detector is operational to observe the neutrinos. With either an idealized detector model or a more realistic model based roughly on the Super-Kamiokande detector, the analysis indicates that if the supernova distance is known, all of the models compared could be distinguished in the case of a supernova distance of 25~kpc, and many for a supernova at 50~kpc. If the distance is unknown, the models could be distinguished at 10~kpc. In addition, assuming an idealized detector, three neutrino oscillation scenarios could be distinguished at 10~kpc. Therefore, the next Galactic core-collapse supernova is likely to provide information on its progenitor star, the high-density nuclear equation of state, and possibly the neutrino mass hierarchy.