Neutrinos are the smallest, yet the most abundant particles in the Universe. They constantly stream through the Cosmos, Earth and everything on it, but rarely interact at all. Neutrinos are much lighter than electrons, and their absolute mass is yet to be measured. Neutrinos may also have another unique feature – a neutrino might be its own anti-particle, a so called Majorana particle. If neutrinos are proven to be Majorana particles, that may provide an answer to one of the biggest puzzles of today: how our universe, and all its matter, came into existence. Although equal amounts of matter and anti-matter were created in the Big Bang, eventually matter prevailed, by a mechanism allowed by neutrino’s Majorana nature. The PI will work on the KamLAND2-Zen experiment, located underground in Japan, that will deploy almost a ton of a Xenon isotope in 1 kilo-ton of liquid scintillator to deliver the most sensitive result in searching for Majorana neutrinos. Looking for rare processes that indicate Majorana nature of neutrino, is challenging due to many similar event signals that are due to noise and backgrounds. Therefore, calibration of the detector response to light is critical to its success. The PI will build the light calibration system for KamLAND2-Zen to characterize the photodetectors’ timing and charge collection, as well as the light transport through different detector volumes. Building the light calibration system will train students and postdocs in designing and build