The neutrino experiments aren't underground to shield them from background neutrinos. There is no way to shield background neutrinos. They are underground to sh

The neutrino experiments aren't underground to shield them from background neutrinos. There is no way to shield background neutrinos. They are underground to shield them from other particles that can produce experimental signatures that look similar to neutrinos. So you're detecting all neutrinos, but you're looking in an energy range where the signal you're interested in rises above the background levels.