Magnetometry for the Nab Experiment*

Nab uses an asymmetric magnetic spectrometer and two large-area segmented Si detectors to extract the neutron beta decay electron-neutrino correlation coefficient \textit{a} and the Fierz interference term \textit{b} from the proton momentum and electron energy spectrum. Nab was designed to achieve a $10^{-3}$ relative uncertainty in \textit{a},  and this requires a detailed characterization and analysis of the magnetic field in the spectrometer. This talk will cover the design and implementation of this field characterization scheme and the current analysis.