Testing silicon detector characteristics and simulating charged particle activity for the Nab Experiment*

Precise measurements of neutron beta decay can be used to expand upon the Standard Model. The Nab Experiment at the Spallation Neutron Source at ORNL will make precise measurements of beta decay by measuring the electron-antineutrino correlation coefficient, a, and the Fierz interference term, b. Variable a is useful for finding the Cabibbo-Kobayashi-Maskawa (CKM) quark-mixing matrix up- to down-quark element Vud. The CKM matrix should be unitary; however, experimental measurements of the top row’s elements disagree with unitarity by over 2??. In the Standard Model, the Fierz interference term b equals zero. The Nab experiment uses a 7 meter-long spectrometer with a silicon detector at each end to measure the electron’s energy and the proton’s momentum. To ensure quality data, we quantified baseline noise for each pixel on each detector. We collected waveform data and processed them. We analyzed the data to determine which pixels are primed for data collection and which pixels have exceptionally high or low noise or are disconnected from their electronics chains. Additionally, we simulated charged particle activity in the detectors with Geant4. Understanding detector characteristics with these studies helps Nab achieve its overall precision goal of Δa/a = 0.001 and Δb = 0.003.