Enhancing the Sensitivity of KamLAND2-Zen Neutrinoless Double Beta Decay Search with Optical Calibrations

About This Grant

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 building new instruments, creating a skilled workforce for tomorrow. The PI will search for neutrinoless double beta decay - the intellectual merit is of the highest caliber and could lead to a revolutionary discovery. KamLAND2-Zen is an upgrade of its successful predecessor KamLAND-Zen which has produced world-leading limits on neutrinoless double beta decay in 136Xe. KamLAND2-Zen will begin data-taking in 2028, with a half-life sensitivity of roughly 2 x 1027 years. The PI will fabricate, install, and commission the optical calibration sources for the KamLAND2-Zen experiment. The PI and her group will enhance the sensitivity of KamLAND2-Zen by building a sophisticated optical model of the Xenon-loaded liquid scintillator, unloaded liquid scintillator, and surrounding buffer oil, in addition to getting precise charge and timing calibration of the PMTs. In turn, the enhanced optical modeling will improve vertex reconstruction for rejection of the backgrounds coming from the target volume boundary and reduce systematic error related to target fiducialization. Specifically, the PI will focus on the fabrication of the fiber-based optical calibration sources, electronic boards needed for light injection with a control box, with support for the team to execute the project. This project will train a postdoctoral associate, and undergraduate students in advanced instrumentation, experimental nuclear physics, and computational modeling, preparing them for leadership roles in STEM. Participants will gain hands-on experience in designing, fabricating, and commissioning a sophisticated optical calibration system, as well as collaborating within the international KamLAND2-Zen collaboration. The project will emphasize comprehensive mentorship, ensuring that team members from receive the support needed to succeed in their roles. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.