First result of a search for Diffuse Supernova Neutrino Background in SK-Gd experiment
Since 2020, Super-Kamiokande (SK) detector has been updated by loading gadolinium (Gd) as a new experimental phase, ‘SK-Gd.’ In the SK-Gd experiment, we can search low-energy electron antineutrinos via inverse-beta decay with efficient neutron identification thanks to high cross-section and high-energy gamma-ray emission of thermal neutron capture on Gd. Until July 2022, the observation is operated with the 0.01% Gd mass concentration. The neutron capture fraction on Gd is about 50% in this situation. In this paper, the first search result for the flux of astrophysical electron antineutrinos for the energy range of O(10) MeV in SK-Gd with a 22.5 × 552 kton·day exposure at 0.01% Gd mass concentration of the initial stage of SK-Gd is reported.