NESSE: a silicon detector simulation Python package for precision beta decay experiments

Many high precision neutron beta decay experiments, such as Nab, UCNB, and BL3, rely on large, thin, highly segmented, ultrapure silicon detectors to precisely detect proton and electron energies and timings. NESSE was developed specifically to simulate the Nab detector signal shape features. In the Nab experiment a proton time-of-flight and electron energy measurements are used to set limits on the angular correlation between the emitted electron and antineutrino in neutron decay, which has implications for CKM unitarity tests. The stringent requirements on the timing bias uncertainty demand a detailed understanding of the timing response of the Nab detectors, providing the driving motivation for NESSE. NESSE primarily calculates charge drift and induced currents, allowing the user to pick their preferred tools to determine electric fields, particle trajectories, and electronic response. Simulated signals from NESSE have been used to characterize Nab detector properties, such as impurity concentration profiles, determine timing biases, and build a library of event signals.