Understanding Silicon Detectors for Precision Beta Decay

The Neutron-a-b (Nab) experiment, hosted at Oak Ridge National Laboratory’s Spallation Neutron Source, provides a high-precision characterization of the weak interaction through free neutron beta decay. Nab aims for a relative precision of 1⋅10^-3 on the angular correlation between beta and neutrino momenta (little-a) and 3⋅10^-3 absolute precision on the Fierz interference term (little-b). These measurements can play a unique role in understanding discrepancies in the current experimental data set for the ratio of axial-vector to vector coupling, and for validating the unitarity of the CKM matrix via determination of V_ud. The experimental apparatus features a specialized detection system designed to precisely capture the energy and timing of decay electrons and protons. This presentation examines the operational principles of our large-area, thick, segmented silicon detectors and the analysis of systematic biases inherent in the detection system. Additionally, it discusses the low-energy steerable proton source at the University of Manitoba, detailing the facility’s capabilities and various studies aimed at characterizing and optimizing detector performance.