A Megaton-Scale Water Cherenkov Neutrino Observatory: Photocathode Coverage, Energy Resolution and Event Rates Computed from Photoelectron Statistics

A next-generation underground neutrino observatory of 260 kilotonnes of water, 190 kilotonnes fiducial, is designed from the statistics of the light it collects. Instrumenting the 22,431 square metres of inner surface at 40 percent photocathode coverage requires 45,696 photomultipliers of 50 cm diameter and yields 6.5 photoelectrons per MeV, from which the energy resolution follows directly: 12.4 percent at 10 MeV and 1.24 percent at 1 GeV. The fiducial volume accumulates 2,280 contained atmospheric-neutrino events per year and about 186 solar-neutrino elastic-scattering events per day. The cavern structure is estimated at 12,500 tonnes and the operating power at 905 kW. Every figure is computed from the stated coverage and yield model; the design is simulated, not measured.