Development of Germanium Ring-Contact Detectors for LEGEND-1000

University Of South Dakota Main Campus, Vermillion SD

Investigators

Abstract

If neutrinos are indeed their own antiparticles, this could explain the prevalence of matter over anti-matter in the universe. Investigating this possibility requires exploring neutrinoless double-beta decay (NLDBD), a possible but rare nuclear decay process. In this context, large germanium (Ge) crystals are excellent detectors of NLDBD due to their high volume-to-surface ratio, which enables effective signal collection and background rejection in the search for NLDBD decay. This NSF-funded project supports the Principal Investigator (PI) and graduate and undergraduate students in conducting research on the development of innovative Ge detectors for the upcoming LEGEND experiment. LEGEND aims to employ ultra-pure Ge detectors and active ways to reject background reactions to search for NLDBD. The PI's role includes training graduate and undergraduate students in novel techniques and equipping them with skills for competitive careers in high-technology fields. Additionally, the PI has implemented an engaging outreach program to foster public interest and understanding in science. The LEGEND Experiment builds upon the advancements made by the MAJORANA Collaboration in ultra-pure materials and the GERDA Collaboration in liquid cryogen active shielding. LEGEND includes a phased deployment of a ton-scale experiment capable of detecting NLDBD events with half-lives exceeding 10e28 years. To reduce backgrounds, complexity, and cost, LEGEND-1000 favors large-size detectors (>3 kg per detector). To explore this approach, the PI will conduct research and development on large-size Ge ring-contact (GeRC) detectors using high-purity Ge crystals grown by the University of South Dakota (USD). Notably, the GeRC detectors can potentially reach sizes exceeding 6 kg, significantly reducing the number of individual detectors required for the LEGEND-1000 experiment. This reduction in detector count will further mitigate backgrounds, elevating the overall sensitivity of the experiment. Collaboration with LEGEND will enable the fabrication and testing of GeRC detectors at USD and other LEGEND institutions. These large-size Ge detectors, incorporating pulse shape discrimination capabilities, will be crucial for further minimizing background events in a ton-scale NLDBD decay experiment like LEGEND. The project not only contributes to advancing our understanding of neutrino properties, such as their Majorana nature and extremely small masses, but also opens doors for exploring new physics at energies beyond the reach of current high energy colliders. Moreover, it has a broader impact by training students in cutting-edge techniques and engaging the public through outreach initiatives. This project is jointly funded by the Nuclear Physics Program and the Established Program to Stimulate Competitive Research (EPSCoR). 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.