Upgrades to the FPGA based Data Acquisition System for the Nab Experiment

Decay correlations in free neutron beta decay serve as a probe of the Cabbibo-Kobayashi-Maskawa (CKM) matrix in the Standard Model and a search for new physics. The Nab experiment will measure the electron-neutrino correlation term, a, and the Fierz interference term, b, by detecting the decay's resulting electrons and protons in coincidence using two 127-pixel Si detectors at each end of the spectrometer. The detector electronics for each pixel continuously sample waveforms at 14 bits and 250 MS/s. This high-volume data stream is processed in real time by FPGAs, which are responsible for implementing a high-efficiency threshold trigger. In this talk, I will present an overview of FPGA firmware improvements that allow us to implement a recursive piecewise polynomial (RPP) filter for a more flexible low-threshold trigger with high efficiency for 30 keV protons. I will also discuss the revamped host software, which has been built from the ground up to take advantage of the new capabilities of the updated firmware.