Low Energy Cross-Calibration of the Hyper-Kamiokande Far Detector Using a Deuterium-Tritium Neutron Generator (DTG)

Hyper-Kamiokande is an international next-generation neutrino experiment currently constructing the biggest detector of its kind; Hyper-Kamiokande Far Detector (Hyper-K) in Japan. The 68m diameter, 71m height cylindrical underground water Cherenkov detector is foreseen to start taking data in 2027 and needs to be calibrated periodically for optimal performance. The primary low energy calibration system will be an electron linear accelerator (LINAC); However, this method suffers from some limitations, namely the anisotropy of the electron beam, the existence of beam pipe while taking data, the limited number of positions where it can be deployed, and it takes a relatively long time to complete the whole process. A DT Generator is used to cross-calibrate the low energy by generating an N16 cloud via (n:p) reactions on O16 after lowering it into numerous positions inside the water tank, the unstable N16 isotope will beta decay isotropically into well-known products and with a half-life of 7.13s allowing us to raise our DTG above the N16 cloud to reduce the optical shadowing of the source before data taking. The N16 could generation and decay are simulated with GEANT4, then the outputs will be propagated through the volume of the detector using the WCSim program (also GEANT4 based). LINAC and DTG were used in the past to calibrate the low energy of Super Kamiokande detector, and they will also be used for Hyper-K.