Double Trapezoid Trigger for the Nab Data Acquisition System

The Nab experiment will determine the neutron decay correlation parameters 'a' and 'b' by reconstructing the full kinematics of each event from the electron energy and proton time of flight. A high efficiency, low energy trigger is needed to detect the protons, which are electrostatically accelerated to 30 keV at the end of the spectrometer to pass through the dead layer of the silicon detector. The logic to determine the timing and energy of both particles is crucial to control systematics associated with particle kinematics. The double trapezoid filter provides energy-independent timing, accounts for ballistic deficit, and subtracts both exponential and constant background. We measured the efficiency of the trigger based on this filter, by simulating the trigger on zero-bias traces.