Characterization of Nab Detector Timing Systematics Using Monte Carlos Simulations*

The Nab Experiment at the SNS in Oak Ridge National Lab aims to measure the electron-neutrino correlation parameter, a, in free neutron beta decay with a precision of Δa/a ≤ 1E-3 using direct measurement of the phase space distribution of the resultant electron energy and proton momentum. The allowable timing systematic, Δt_{proton-electron}, must be less than a 300 ps deviation from the average to meet this goal. In measuring tagged particles, particularly electrons, across a broad range of energy, we can gain an understanding of how the detector physics will affect the timing measurement and set a limit on Δt_{proton-electron}. Electron-capture sources produce fixed energy electrons with a well-understood "tag" from coincidence photons. Using a fast CeBr3 scintillator with a SiPM readout, we can measure the systematic effects associated with the Nab silicon detectors. We present here an analysis of Monte Carlo simulations for ¹³⁹Ce, ¹³³Ba, and ¹¹³Sn decays, and discuss the application of these results to the experiment as a whole.