Characterization of a Fast Gamma Timing Detector for the Nab Experiment*

The Nab experiment aims to test the standard model of particle physics by studying the kinematic constants of neutron beta decay. Namely, Nab is studying a, the correlation angle between the electron and neutrino, and b, the Fierz interference term. These parameters must be measured with high precision to sensitively test the standard model. Nab utilizes a long spectrometer that measures the time-of-flight (TOF) the proton from neutron decay and therefore its momentum.  The uncertainty of the average TOF of protons between detectors must be less than a nanosecond. To characterize the Nab silicon detectors, we will be performing in-situ timing studies using fast gamma timing detectors to measure the electron/gamma coincidence from multiple radioactive sources. Two detectors of interest are Cerium Bromide (CeBr3) and Barium Fluoride (BaF2). We have performed multiple timing studies using a source of Cobalt-60 and Europium-152 with CeBr3 detectors, and have also assembled a dual-PMT BaF2 detector to be used in further tests. In this talk we will discuss the energy and time calibrations of the detectors along with future work at Oak Ridge.