Pile-Up Waveform Filter for the Nab Experiment*

The Nab experiment is measuring the electron-neutrino correlation term, along with
the Fierz interference term, within the theory of neutron beta decay. The electron-
neutrino correlation parameter will be measured with a relative uncertainty of
10-³, and the Fierz interference term with an uncertainty of ~3 x 10-³. Data
collection will begin in the Spring of 2019 at the fundamental physics beamline of
ORNL's SNS. Two segmented, large area, Si detectors will be used with a total of
254 pixels instrumented. A method for identifying potential pile-up and accidental
signals will be discussed, this being vital for precise energy reconstruction. In
this method, multiple trapezoidal filters and a post-filter identification
algorithm have been optimized for the expected waveform features. A
characterization of each trapezoidal filter has been performed with a simulated
data set, with plans to use this method to characterize a beta decay dataset from
⁴⁵Ca and other sources, taken using Nab detectors in 2017.