Performance of the Detection System for the Nab Experiment

The decay of free neutrons enables precise studies of CKM unitarity, by measuring V_ud, and searches for beyond the Standard Model physics such as weak scalar and tensor interactions. The goal of the Nab experiment, operated at the Spallation Neutron Source at Oak Ridge National Laboratory, is to measure the electron-neutrino correlation coefficient, a, and the Fierz interference term, b, to a precision Δa/a = 0.1% and Δb = 0.003, respectively, via beta decay of cold free neutrons. Nab uses two 128 channel detection systems based on silicon detectors with fast timing (10s of ns) and good energy resolution (few keV) to meet requirements for detecting and processing signals from decay electrons and protons. The system must also operate with minimal electronic and thermal noise, high voltage, and maximal detector temperature stability. The summer 2023 commissioning run successfully demonstrated working operation of the experiment. However, some shortcomings within the electronics assembly were identified. Therefore, a campaign to address the design, layout, and implementation of the electronics system has been launched. I will present an overview of the detection system, progress made in their commissioning and the electronics overhaul campaign, and details of their performance in the Nab experiment.