Supernova Neutrino Spectra and Applications to Flavor

We study the flavor-dependent neutrino spectra formation in the core of a supernova (SN) by means of Monte Carlo simulations. Several neutrino detectors around the world are able to detect a high-statistics signal from a galactic SN. From such a signal one may extract information that severely const...

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Bibliographic Details
Main Author: Keil, Mathias Thorsten
Other Authors: Drees, Manuel (Prof. Dr.), Lindner, Manfred (Prof. Dr.)
Format: Doctoral or Postdoctoral Thesis
Language:English
Published: Technical University of Munich 2007
Subjects:
Online Access:http://mediatum.ub.tum.de/node?id=602976
http://mediatum.ub.tum.de/doc/602976/document.pdf
http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:91-diss2003072214096
Description
Summary:We study the flavor-dependent neutrino spectra formation in the core of a supernova (SN) by means of Monte Carlo simulations. Several neutrino detectors around the world are able to detect a high-statistics signal from a galactic SN. From such a signal one may extract information that severely constrains the parameter space for neutrino oscillations. Therefore, reliable predictions for flavor-dependent fluxes and spectra are urgently needed. In all hydrodynamic simulations the treatment of nu_mu,tau and nu_mu,tau-bar is rather schematic, with the exception of the most recent Garching-Group simulation, where the interaction processes were updated partly based on our results. The interactions commonly included in traditional simulations are iso-energetic scattering on nucleons, scattering on electrons and positrons, and electron-positron pair annihilation. In our Monte Carlo simulations we vary the static stellar background models in addition to systematically switching on and off our set of interaction processes, i.e., recoil and weak magnetism in N nu -> nu N, scattering on electrons and positrons and nu_e/nu_e-bar, electron-positron and nu_e-nu_e-bar annihilation into nu_mu,tau nu_mu,tau-bar pairs, and neutrino bremsstrahlung off nucleons. As nu_mu,tau and nu_mu,tau-bar sources, bremsstrahlung and electron-neutrino pair annihilation dominate. The latter process has never been studied before in the context of SNe and turns out to be always more important than the traditional electron-positron-annihilation process by a factor of 2-3. For energy transfer, the most important reactions are scattering on nucleons with recoil, and scattering on electrons and positrons. Weak magnetism has a very small effect and scattering on nu_e and nu_e-bar is negligible. The beta processes dominate for nu_e and nu_e-bar. In comparing our numerical results for all flavors we find the standard hierarchy of mean energies nu_e < nu_e-bar < nu_mu,tau, with, however, very similar values for nu_mu,tau and nu_e-bar. The luminosities of nu_mu,tau and nu_e-bar can differ by up to a factor of 2 from L_nue-bar = L_nue. The Garching Group obtains similar results from their self-consistent simulation with the full set of interactions. These results are almost orthogonal to the previous standard picture of exactly equal luminosities of all flavors and differences in mean energies of up to a factor of 2. Existing concepts for identifying oscillation effects in a SN neutrino signal need to be revised. We present two methods for detecting the earth-matter effect that are rather independent of predictions from SN simulations. An earth-induced flux difference can be measured by the future IceCube detector in Antarctica and a co-detector like Super- or Hyper-Kamiokande. At a single detector with high energy resolution the Fourier transform of the inverse-energy spectrum can reveal the modulations of the spectrum. Both methods are sensitive to the small mixing angle theta_13 and the neutrino mass hierarchy. In einer systematischen Studie untersuchen wir den Einfluss aller relevanten Neutrino-Materie-Wechselwirkungen und stellarer Profile auf die Emission von Neutrinos von Supernovae (SNe). Unsere Studien zeigen, dass in allen bisherigen Modellen dominierende Reaktionen vernachlässigt wurden. Simulationen, die alle relevanten Wechselwirkungen enthalten, finden wesentlich ähnlichere Spektren für Elektron- und Müon-Antineutrinos als bisher angenommen, wobei sich die Teilchenflüsse aber erheblich unterscheiden. Diese beiden Neutrino-Arten sind relevant für die Messung von SN-Neutrinos, da Detektoren nur Elektron-Antineutrinos mit hoher Effizienz messen können, deren Spektren im Detektor aber bedingt durch Oszillationen eine Mischung der ursprünglichen Elektron- und Müon-Antineutrino-Spektren darstellen. Deshalb müssen frühere Vorhersagen über Oszillations-Effekte in SN-Neutrino-Spektren den neuen Ergebnissen angepasst werden. Wir schlagen zwei Methoden zur Identifizierung des Erd-Effeks vor.