Towards Polarimetry for the Nab Experiment

The Nab experiment at the Fundamental Neutron Physics Beamline (FnPB) at the Spallation Neutron Source (SNS) aims to make precision measurements of the electron-neutrino correlation, a, and Fierz interference term, b, associated with the beta decay of free neutrons. Tiny residual polarization of the incident beam presents a potential source of systematic error in the measurement of a. In order to understand and mitigate these effects we must measure the beam polarization and the efficiency of our neutron spin flipper. If we use $^3$He polarizers to accomplish these measurements, it will require careful control of the magnetic environment along the beam, in order to both assure adiabatic spin transport of the neutrons, and prolong the polarization lifetime the $^3$He cells. However the space for incorporating the necessary components is limited, and requires the use of novel approaches to magnet construction to obtain the requisite fields. This talk will describe the polarimetry setup and simulated spin transport results.