Diffuse neutrinos from luminous and dark supernovae: prospects for upcoming detectors at the O(10) kt scale

We estimate the Diffuse Supernova Neutrino Background (DSNB) using the simulation results for neutron star-forming and black hole-forming stellar collapses from the Garching group. Scenarios with different distributions of black-hole forming collapses with the progenitor mass are discussed, and the uncertainty on the cosmological rate of collapses is included. The electron antineutrino component of the DSNB above 11 MeV of energy is found to be ~(1.4 - 3.7) cm^-2 s^-1; the contribution of black hole-forming collapses could dominate the flux above ~25 MeV. We calculate the potential of detecting the DSNB at SuperK-Gd and JUNO, in about a decade-long period of operation. We find that, in our model, it is likely that a significant excess above the background will be obtained at JUNO, while detection will be more difficult at SuperK-Gd. The potential when the two experimental results are examined jointly is discussed as well. We also consider an example of a future O(10) kt slow liquid scintillator detector, and show that there the odds of detection are very good. Our results motivate experimental efforts in reducing the backgrounds due to neutral current scattering of atmospheric neutrinos in SuperK-Gd.