An In-situ Timing Apparatus for the Nab Experiment

The Nab experiment seeks to probe the weak interaction through the fundamental nature of neutron beta decay in order to discover potential new physics beyond the standard model. Nab will carry out high precision measurements of the electron-neutrino correlation parameter, a, and the Fierz interference term, b, by measuring the electron energy and proton time-of-flight which allows for estimation of the proton momentum. To make measurements of the precision required, Nab demands the average proton time-of-flight to be known with an uncertainty of less than 1 ns. The timing of the Nab Si detectors will be characterized through multiple methods, but we will be focusing on an in-situ timing study using a gamma detector (BaF2 or CeBr3) as an electron/gamma coincidence tag from radioactive sources for the Si detectors. We will present coincidence timing studies from BaF2 and CeBr3 and simulations of electron and gamma transportation in the spectrometer.