The Majorana neutrinoless double-beta decay experiment

Abstract

The Majorana project is a next-generation neutrinoless double-beta decay (Oνββ) experiment that will endeavor to provide evidence as to the Majorana or Dirac nature of the electron neutrino. If the neutrino is a Majorana particle, Oνββ measurements will also provide direct limits on the effective Majorana mass (⟨mββ⟩) of the electron neutrino. We present an overview of current plans to build a ‘demonstrator module’ with an active mass of ≈ 60 kg (30 kg of this will be natural germanium, and 30 kg will be enriched to 86% in 76Ge). This mass corresponds to a sensitivity to ⟨mββ⟩ ≈ 200 meV, assuming light Majorana neutrino exchange dominates as the mechanism for Oνββ. This phase of the Majorana experiment will demonstrate the background levels and experimental techniques necessary to scale up to an detector fielding an active mass of 1000 kg of 76Ge (corresponding to ⟨mββ⟩ sensitivity of ≈ 30 meV). Detector fabrication is a critical issue for performance, cost, and schedule of a 1000-kg detector array, and the collaboration is examining alternative detector technologies including both point-contact p-type and highly-segmented n-type diodes during the demonstrator phase of the experiment. We will highlight recent Majorana technical and R&D achievements and outline a path forward for construction of the demonstrator module.