Detection of a single electron produced inside bulk superfluid helium

The HERON project is an effort to develop a detector for low-energy solar neutrinos in real time by observing their elastic scattering from electrons using superfluid helium as the target material. By applying appropriate electric fields, the recoil electron can be separated from the positive ion, drifted upward to the liquid–vacuum interface, transmitted through the surface with the aid of a vortex ring, and detected using a calorimeter. By studying the correlation of the 16 eV photon signal produced by scintillation and the single-electron signal, we can locate a neutrino event in a large detector and distinguish it from the background events involving multiple Compton scattering.