Speakers
Description
In this presentation we report the study for searches for high-energy astrophysical electron neutrinos ($ν_e$) above 10 GeV using an optimized selection criterion in Super-Kamiokande (SK).
Potential sources of high-energy astrophysical neutrino include galactic plane, active galactic nuclei such as NGC 1068, as well as specific types of supernovae with structure of circumstellar material. Some of them have coincident neutrino being observed with energy above TeV. Though models predict a continuous spectra of neutrino emission that extends to energy scale of GeV, no excess have been found over atmospheric neutrino background. Current searches focus on muon neutrinos ($ν_μ$), yet if we measure the ratio of astrophysical $ν_e$ and $ν_μ$ fluxes on Earth, we can constrain the neutrino flavor compositions at source, providing better understanding of acceleration mechanism of cosmic rays. More than 26-year long period observed data from SK provides opportunity for searches in coincidence with these sources.
Good direction and energy reconstruction of high-energy $ν_e$ events in SK enables point source searching and spectrum fitting. Angular resolution for fully contained (FC) events, in which most $ν_e$ goes, is smaller than 10°, and we can reduce backgrounds by focusing on specific area in sky. SK also have sensitivity to $ν_e$ coming from any direction, which allows us to perform search for any position in sky. Additionally, $ν_e$ has lower background from atmospheric neutrinos compare with $ν_μ$, since atmospheric $ν_e$ flux at 100 GeV is only 1/10 of $ν_μ$ flux, and spectrum of atmospheric $ν_e$ is softer than $ν_μ$. As a result of the reasons described above, we aim to search for astrophysical $ν_e$ over atmospheric neutrino background in high energy region in SK.
One of the challenges in searching for high-energy astrophysical $ν_e$ we are facing is the contamination of $ν_μ$ events. We will optimize selection criterion by using reconstructed variables including number of Cherenkov radiation ring, number of decayed electrons and distance to the boundary of the detector with Monte Carlo simulations. Such selection criterion is expected to improve event-identification of $ν_e$ and $ν_μ$ events through charged current interactions as well as events undergo neutral current interactions and improve purity of $ν_e$ events. Based on this selection criterion we will study the sensitivity of $ν_e$ detection and use unbinned maximum likelihood to search for high-energy astrophysical $ν_e$ in SK.
| Collaboration(s) | The Super-Kamiokande Collaboration |
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