Indication of Electron Antineutrinos from the Diffuse Supernova Neutrino Background

We report an indication of $\barν_e$ 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 $ν$ 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 $3.6^{+1.6}_{-1.5}~\mathrm{cm^{-2}\,s^{-1}}$ for $E_ν>13.3$~MeV, corresponding to a $2.6σ$ tension with a null hypothesis ($99.5\%$ C.L., one-sided). Similar significances were obtained with signal models of varying spectral shapes.