NDEx-100 conceptual design report

Observing nuclear neutrinoless double beta (0v beta beta) decay would be a revolutionary result in particle physics. Observing such a decay would prove that the neutrinos are their own antiparticles, help to study the absolute mass of neutrinos, explore the origin of their mass, and may explain the matter-antimatter asymmetry in our universe by lepton number violation. We propose developing a time projection chamber (TPC) using high-pressure (SeF6)-Se-82 gas and Topmetal silicon sensors for readout in the China Jinping Underground Laboratory (CJPL) to search for neutrinoless double beta decay of Se-82, called the N nu DEx experiment. Besides being located at CJPL with the world's thickest rock shielding, N nu DEx combines the advantages of the high Q(beta beta) (2.996 MeV) of Se-82 and the TPC's ability to distinguish signal and background events using their different topological characteristics. This makes N nu DEx unique, with great potential for low-background and high-sensitivity 0v beta beta searches. N nu DEx-100, a N nu DEx experiment phase with 100 kg of SeF6 gas, is being built, with plans to complete installation at CJPL by 2025. This report introduces 0v beta beta physics, the N nu DEx concept and its advantages, and the schematic design of N nu DEx-100, its subsystems, and background and sensitivity estimation.