LEGEND-1000: Engineering the Near-Zero Background Environment for 0νββ Discovery

Unambiguous discovery of neutrinoless double-beta decay (0νββ) requires unprecedented control and mitigation of background contribution in the region of interest. The LEGEND collaboration aims to achieve a discovery sensitivity of T_1/2>10²⁸ years with the high-purity germanium (HPGe) isotope ⁷⁶Ge (Q = 2039 keV). The initial phase, LEGEND-200, is operational at Laboratori Nazionali del Gran Sasso (LNGS), utilizing up to 200 kg of HPGe detectors immersed in liquid argon (LAr), which acts as both a coolant and an active shield. The subsequent phase, LEGEND-1000 (scheduled for construction in late 2026), will scale up to 1000 kg and demands a strict background contribution of less than 10^-5 cts/(keV kg yr) at the Q-value. To meet this stringent requirement, our R&D is focused on advancing radiopure component design, including the selection of ultra-radiopure materials, the exploration of optically active enclosures, and the implementation of specialized pulse shape discrimination. Furthermore, we are developing novel detector component materials utilizing additive manufacturing (3D printing) to reduce intrinsic background radiation and optimize component functionality. This presentation will provide comprehensive insights into the LEGEND-1000 baseline design and detail the various background reduction and material development techniques being deployed to enable the next generation of 0νββ discovery.