Supernova Relic Neutrino search with neutron tagging at Super-Kamiokande-IV

Abstract A search for Supernova Relic Neutrinos ν ¯ e ’s is first conducted via inverse-beta-decay by tagging neutron capture on hydrogen at Super-Kamiokande-IV. The neutron tagging efficiency is determined to be ( 17.74 ± 0.04 stat . ± 1.05 sys . ) % , while the corresponding accidental background probability is ( 1.06 ± 0.01 stat . ± 0.18 sys . ) % . Using 960 days of data, we obtain 13 inverse-beta-decay candidates in the range of E ν ¯ e between 13.3 MeV and 31.3 MeV. All of the observed candidates are attributed to background. Upper limits at 90% C.L. are calculated in the absence of a signal.