Supernova neutrinos in SK-Gd and other experiments

Now many detectors are waiting for core-collapse supernovae in or near our galaxy. If they occur in our galaxy we will be able to reveal the mechanism of supernova explosions and also be able to access the properties of neutrinos, such as mass hierarchy. Even dark mater detectors can reach them via coherent elastic neutrino nucleus scattering; however no supernova neutrinos have been observed since February 1987. Supernova explosions in our galaxy may be fairly rare, but supernovae themselves are not. On average, there is one supernova somewhere in the universe each second. The neutrinos emitted from all of these supernovae since the onset of stellar formation have suffused the universe. We refer to this unobserved flux as the “relic” supernova neutrinos. Theoretical models vary, but several supernova relic neutrinos (SRNs) per year above 10 MeV are expected to interact in Super-Kamiokande. However, in order to separate these signals from the much more common solar and atmospheric neutrinos and other backgrounds, we need a new detection method. On June 27 2015, the Super-Kamiokande Collaboration approved the SK-Gd project. It is the upgrade of the SK detector via the addition of gadolinium sulfate. This modification will enable it to efficiently identify low energy anti-neutrinos for the world’s first observation of the SRNs via inverse beta decay.