A self-calibrating pulse-shape discriminator for identifying neutrinoless double-beta decay events in HPGe spectrometers

Pulse-shape discrimination (PSD) for germanium spectrometers has received attention for varied applications such as microphonic noise rejection, event localization in segmented detector systems, correction of ballistic deficit and trapping, and the separation of gamma events from nuclear recoil and beta decay. A new PSD method has been developed at Pacific Northwest National Laboratory (PNNL) having several unique characteristics. This PSD method: 1) Extracts a few key parameters from each preamplifier output pulse. 2) Is sensitive to interaction multiplicity - a new physical observable. 3) Can isolate various physical regions of a detector. 4) Is self-calibrating allowing optimal discrimination for any detector. 5) Is computationally cheap, requiring no computed libraries-of-pulses. 6) Leverages current state-of-the-art commercial digital spectroscopy hardware platforms. This paper describes the theory and operation of the method with attention to specific application areas in which this method could be useful. The challenge of sensing the neutrinoless double-beta decay of ⁷⁶Ge (Oν ββ-decay) is taken as an example of a single-site-interaction measurement. Experimental data is analyzed and the sensitivity increase expected from this method for neutrino mass probes based on Oν ββ-decay is presented.