Title: Understanding the Nature of Neutrinos via Neutrinoless Double Beta Decay

Speaker: Wenqin Xu (University of South Dakota)

Abstract:Neutrinos provide a critical portal to physics beyond the Standard Model, but many neutrino properties are still largely unknown. The seesaw model can readily explain the small but non-zero neutrino mass and it requires neutrinos to be Majorana particles, i.e. fermions that are their own antiparticles. Neutrinoless double beta (0νββ) decay is a hypothetical lepton-number-violating process that is possible only if neutrinos are Majorana particles. The discovery of 0νββ decay would unambiguously establish the Majorana nature of neutrinos and explicitly show that the total lepton number is violated. A measurement of the decay rate may yield information regarding the absolute neutrino mass.

Deploying 44 kg of high-purity Germanium (HPGe) detectors at the 4850′ level of the Sanford Underground Research Facility in South Dakota, the Majorana Demonstrator (MJD) experiment is an ultra-low background experiment searching for  0νββ decay in ⁷⁶Ge. The construction and commissioning of MJD has completed and the multiple-year data-taking has started. At the meantime, more than 200 researchers around the world, including many Majorana collaborators, have formed a new collaboration for the Large Enriched Germanium Experiment for Neutrinoless Double Beta Decay (LEGEND). The LEGEND collaboration aims to develop a phased, ⁷⁶Ge based 0νββ decay experimental program with discovery potential at a half-life beyond 10²⁸ years. In this talk, we will review the physics of 0νββ decay. We will discuss initial results from the Majorana Demonstrator experiment and the status of the LEGEND project.