WATCHMAN is a WAter Cherenkov Monitor for ANtineutrinos.
The baseline WATCHMAN design is a kiloton scale gadolinium-doped (Gd) light water Cherenkov detector, placed several kilometers from a civil nuclear reactor.
In its first deployment phase, WATCHMAN will be used to remotely detect a change in the operational status of the reactor, providing a first-ever demonstration of the potential of large Gd-doped water detectors for remote reactor monitoring for future international nuclear nonproliferation applications.
During its first phase, the detector will provide a critical large-scale test of the ability to tag neutrons and thus distinguish low energy electron neutrinos and antineutrinos.
This would make WATCHMAN the only detector capable of providing both direction and flavor identification of supernova neutrinos. It would also be the third largest supernova detector, and the largest underground in the western hemisphere.
WATCHMAN will also be a major integration platform for a host of technologies relevant for the Long-Baseline Neutrino Facility (LBNF) and other future large detectors.