First study of neutron tagging with a water Cherenkov detector

A first study of neutron tagging is conducted in Super-Kamiokande, a 50,000 ton water Cherenkov detector. The tagging efficiencies of thermal neutrons are evaluated in a 0.2% GdCl3GdCl3-water solution and pure water. They are determined to be, respectively, 66.7% for events above 3 MeV and 20% with corresponding background probabilities of 2×10-42×10-4 and 3×10-23×10-2. This newly developed technique may enable water Cherenkov detectors to identify ν¯e’s from astrophysical sources as well as those produced by commercial reactors via the delayed coincidence scheme.