Characterizing the AFP Spin Flipper for the Nab Experiment

The Nab experiment, operated at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL), aims to measure with high precision the electron-neutrino correlation parameter a and the Fierz interference term b with protons and neutrons emitted from free and unpolarized neutron β-decay. To eliminate a significant source of systematic error, the admixture from other correlation parameters with a, the neutron beam must remain unpolarized with a value less than P_n = 2 x 10^-5. To characterize the polarization of the neutron beam, the Nab experiment uses a polarized ³He spin filter as an analyzer and an Adiabatic Fast Passage (AFP) neutron spin flipper to depolarize the beam. Here, we describe the efforts to characterize the efficiency of the spin flipper used in the Nab experiment.