Effects of Neutrino Oscillation on the Supernova Relic Neutrino Background
arXiv:hep-ph/9609241 · doi:10.1142/S0218271896000321
Abstract
We investigate to what extent the oscillation or conversion of neutrinos enhances the expected event rate of the supernova relic neutrino background (SRN) at the Super-Kamiokande detector (SK). The SRN \barν_e's can be almost completely exchanged with ν_μ-like neutrinos by the MSW oscillation under the inverse mass hierarchy with Δm^2 ~ 10^{-8}--10^5 [eV^2], or by the magnetic moment of Majorana neutrinos with μ_ν>~ 10^{-12} μ_B and Δm^2 ~ 10^{-4}--10^0 [eV^2]. In the standard calculation of the SRN flux, the event rate of the SRN \barν_e's at the SK in the observable energy range of 15--40 MeV can be enhanced from 1.2 yr^{-1} to 2.4 yr^{-1} if all \barν_e's are exchanged with ν_μ-like neutrinos. The enhancement is prominent especially in the high energy range (\gtilde 25 MeV). In the astrophysically optimistic calculation, the event rate becomes as high as 9.4 yr^{-1}. Because the theoretical upper bound of the SRN events without oscillation is about 5 yr^{-1} taking account of the various astrophysical uncertainties, we might have to resort to the neutrino oscillation if more than 5 events in a year, as well as a significantly harder spectrum, were observed in the SK.
arXiv comment10 pages, 3 postscript figures included