Indication of Electron Antineutrinos from the Diffuse Supernova Neutrino Background

Abstract

We report an indication of ${\bar{\nu }}_e$ from the diffuse supernova neutrino background (DSNB) based on a spectral fit analysis of a 5003.0-day dataset in Super-Kamiokande. Key improvements over previous searches include enhanced rejection of atmospheric $\nu$ backgrounds, updated evaluations of systematic uncertainties, and a refined spectral fitting method. Using a representative DSNB model, the best-fit flux was determined to be $3.6_{-1.5}^{+1.6}\mathrm{c}{\mathrm{m}}^{-2}{\mathrm{s}}^{-1}$ for $E_{\nu }>13.3$~MeV, corresponding to a $2.6\sigma$ tension with a null hypothesis ($99.5\%$ C.L., one-sided). Similar significances were obtained with signal models of varying spectral shapes.

arXiv comment14 pages, 9 figures, 3 tables